I am a building designer. First, it is not easy and involves a lot of knowledge and skills. While there isn't any "licensing" requirements to be a building designer, it does not mean it is lawful for you to offer to design buildings for clients without possessing the knowledge and skills. That would fall into 'fraud' and 'misrepresentation'. There is a set of knowledge and skills you need to have that is separate from construction trades & skills. Construction trades & skills is not the same as designing. Just because you can build doesn't mean you can design and vice versa. Professionally, it would be good to have some knowledge and skills in construction when designing.
There is a building designer certification program and a title (which you can not legally use unless you have the certification). While 'anyone' can call themselves a building designer, only those certified by the NCBDC council of the American Institute of Building Design, to use the title "Certified Professional Building Designer" and the acronym (CPBD) when used as abbreviation for the full title. This is protected under some federal laws (trademark) so this legal protections is effectively equivalent to a title law. Regardless of the certification itself, there was a "job tasks analysis" done that involved input from hundred of designers around the nation and that input becomes part of the listed knowledge areas and so forth.
CPBD Candidate Handbook:
https://cpbd.info/chb.pdf
As an FYI: A building designer needs to be professionally competent in knowledge and associated skills in these following areas (drawn from the CPBD candidate handbook - pages 39-43 ):
Business Administration:
A. Ethics
- AIBD (and other professional standards regarding ethics) Code of Ethics
- Copyright registration (to protect your intellectual property rights)
- Federal copyright law (to protect your intellectual property rights and respect the intellectual property rights of others)
B. Licensure
- State business licensing or registration
- County business license/tax
- Municipal business license/tax
- Architectural/Professional business licensing
C. Insurance
- General liability
- Workers compensation
- Health Benefits
- Errors & Omission (professional liability) insurance and related legal issues.
D. Employment Laws
- Federal employment laws and compliances
- State/Provincial & regional employment laws and compliance
- Copyright issues relating to "Work for Hire" (employment) and subcontractors/consultants.
E. Accounting
- General accounting principles (eg. book keeping, profits & loss statements, balance sheet, income statements)
- Federal tax requirements
- State/Province tax requirements
- Local tax requirements
F. Marketing
- Marketing plan creation (would relate with business plan)
- Social media (we're in the 21st century, after all)
- Networking (not IT networking but marketing network and establishing of professional networking)
- Advertising
Business Practices
A. Project Management
- Quality Standards
- Quality Control
- Project design budgeting (ie. direct design costs and expenses)
B. Programming and Due Diligence (Project program.... scope of work, criteria, etc. NOT software programming)
- Scheduling
- Communications (eg. RFIs, change orders)
C. Contracts
- Clients (Design Professional -- Client contracts)
- Employees (employment contracts from traditional to special contracted employment contracts)
- Sub-contractors & consultants (the people you subcontract with such as consultants [engineers, historic preservation consultants, architects, etc.]
- Lien rights
Design Process
A. Concept Development
- Criteria Development (relating to programming)
- Conceptual plans
- Preliminary design(s)
- Concept modification (design development)
B. Construction Document Development
- Working Drawings (part of the technical submittals and all)
- Support documents/specifications
C. Contract Completion
- Publishing/Release for Constructions
- Design Fee (methods of pricing and how to price your services)
Building Design
A. Building Planning
- Code scope (building codes, energy codes, etc.), administration, and definitions
- Wind loading design and criteria (designing for wind conditions and performance criteria meeting codes, standards, etc.)
- Snow loading design and criteria (designing for the weight of snow in the locale of project and performance criteria)
- Seismic category design & criteria (as in seismic designing per criteria of seismic category and performance criteria)
- weathering design / criteria
- Room dimensions, egress requirements, clearances, minimum room sizes, and ceiling height | occupant load
- life safety criteria (e.g. glazing, guards, and fall protection)
- light, ventilation, heating, and sanitation
- flood & termite protection
- designing of garages, carports, and storm shelters and associated performance criteria & codes and standards requirements
- Elevators & lifts
- Accessibility
- consistent drafting standards (e.g. ANSI drafting standards, Architectural Graphics Standards, etc.)
B. Site Design
- Zoning compliance
- Curb cuts public access
- driveways and off street public access
- public utilities (ie. available services, accessibility)
- On-site Utilities
- Site orientation (e.g. viewscapes, solar, ventilation)
- Soil characteristics and bearing capacity
- Cut/Fill/Balance grading
- Erosion control
- stormwater management
- hardscape landscaping / design
- greenscape landscapeing / design
C. Foundations, Concrete, Structural Masonry
- Concrete characteristics and structural performance
- mortar characteristics and structural performance
- footing type, sizes, and applications
- wall and pier applications
- Flatwork applications (floors, driveways, patios, etc.)
- Subgrade drainage and associated solutions
- Radon mitigation and associated solutions
- waterproofing and associated solutions
- anchorage and associated solutions
- material expansion/contraction and associated solutions
- reinforcement and associated solutions
- moisture control and associated solutions (eg. capillart breaks, vapor barriers, etc.)
- backfill and associated solutions (eg. membranes, french drains, gravel, etc.)
D. Framing Systems (knowing types of framing systems, how to design, and apply them in practice on a professional level)
- dimensional lumber characteristics and structural performance (especially know how to size and use of load/span tables)
- engineered lumber characteristics and structural performance
- structural panels characteristics and structural performance
- trusses characteristics and structural performance
- connectors characteristics and structural performance
- applied solutions characteristics (e.g. fundamental structural design, basic load calculations, load-path tracing, etc.)
- braced wall systems structural design
- seismic structural concepts
- continuous load paths tracing
- advanced framing design
- floor systems
- wall types and application
- ceiling types and application
- roof styles, types, and systems
E. Thermal & Moisture Protection
- lightweight all cladding
- stucco (and EIFS) wall cladding
- masonry veneer wall cladding
- shingles roofing
- metal roofing
- tile roofing
- membrane roofing
- gutters and downspouts
- roofing underlayment
- vapor barriers and retarders
- flashing
- drainage planes
- insulation materials
- insulation properties
- doors and egress
- windows, fenestration and egresss
- skylights, fenestration and egress
- air distribution & mechanical systems
- hydronic distribution & mechanical systems (eg. geothermal heating, radiant slab)
- ventilation systems (e.g., kitchen/bath ventilations, whole house heat exchange)
- Fireplaces and wood stoves mechanical systems
- natural ventilation systems (e.g. skylights, cross ventilation, clerestory)
F. Mechanical, Electrical, Plumbing
- Interior water distribution plumbing systems
- water heating plumbing systems
- drain, waste, and vent plumbing systems
- sewer connection or septic plumbing systems
- fixtures plumbing systems
- electrical service entrances
- electrical grounding
- schematical electrical layout (e.g. device & fixture locations)
- electrical circuit control, arc, and ground fault control
- electrical branch wiring
- electrical devices
- electrical fixtures
- conduction heat flow
- convection heat flow
- radiant heat flow
- vapor drive/vapor flow
- vapor accumulation and condensation
G. Building Science, and Sustainability
- air tightness (e.g., air barrier, envelope integrity, blower door testing)
- indoor air quality
- life cycle analysis resource efficiency
- waste mitigation-recycling resource efficiency
- local sourcing resource efficiency
- material certification and content analysis resource efficiency
- LEED-H green building programs, criteria, standards, design
- NAHB green building programs, criteria, standards, design
- local green building programs, criteria, standards, design
- Passive based solar design and Passive House programs, criteria, standards, and design (I argue passive & active solar design
principles, standards, performance characteristics, criteria, etc.)
- Energy star green building program
H. Domestic Architecture
- Climate, technology, and traditions (My added point: also including historic preservation, restorations, rehabilitation, adaptive re-use standards, architectural styles, and proper methods of treatment of historic buildings, the context of climate, and technology)
There is other areas not listed that may be appropriate for a building design professional to have knowledge and skills in regards to local needs. The building designer would need to develop knowledge and skills in most of those areas over the course of working for others, self-study, and/or experience. Forget what HGTV may make it seem like it's magic like a little snap the fingers and it suddenly happens.
There is overlap with construction but you got to look at it from the view point of 'designing' versus building.