In 2020 I built a 30x50 with 15' walls. Others have already mentioned a slab, as long as it's to size and square the building should fit with the siding overlapping the edge. Build it with footings to match your frost line (12", no frost line in SC). Be careful about putting in conduit for future electric or other services. In some zoning areas this turns your slab into a foundation: building permits get more complicated which always runs up construction cost. That was the case here.
I noticed you have no insulation. The lowly R-5 bubble insulation is wonderful in my building in this area. Temperature change indoors is gradual, there is no sweating, and definitely no "rain" inside our building. It will be easy to control temperature and humidity once heat and a/c is installed.
You may want a few more windows. I put mine (5) at the 10' level, they let light in while too high for prying eyes.
I noticed you only spec'd one 10x10 door. I have 3; two on the end and one in the side. It makes a tremendous difference in ventilation.
The upgrade to 12 guage is not too expensive, you might consider that for a building as large as yours will be. They can also double-up the uprights for a nominal fee.
I hope this helps, these were all items I spec'd for my building and am happy I did.
Lou Manglass