Can I just purchase a generic set of plans from a website for my home?

Unfortunately generic plans you see on websites for sale may be good for initial ideas, but every city has extremely specific requirements requiring many details that these plans are missing such as:

1. A site plan designed over a survey for your actual lot which will need to include a drainage plan, landscape plan, specify setbacks unique to your lot, indicate any protected trees on your site,indicate your driveway, driveway apron, and impervious area.

2. Construction details specific to your city's wind exposure, soil type, and zoning requirements

3. Floor plan that will have to conform to your specific zoning requirements which may include transparent fenestration with respect to the number of windows.

4. Foundation plan with footings designed & engineered to soil type and amount of load bearing weight.

5. Cell layout

6. Elevations designed with respect to zoning requirements specific to your city

7. Roof plan designed & engineered to your specific code requirements & wind speed 

8. Truss layout & engineering specific to wind speed & exposure.

9. Lintel Layout for all windows & doors

10. Structural details specifically engineered to your unique home and building code requirements

11. Flashing details for windows & doors

12. Electrical layout