They are never big enough. With what you want to put in. 48x48 stick built not a pole. I used 12 ft lumber on a 18 high wall . Gave me 13.6 . room for a lift. Then I build a second floor around the lift and put a crane in. Mine is 32 wide by 48 deep I should have went the extra 16 ft.
When I poured the walls I did a 2x2 footer with a 4 ft wall on top and a 8 inch floor. . This way in the future I would have the foundation strength to add on going up. And I did. Now I want to add on for a place to keep cars. Thinking of a 4 post to put cars upstairs. This should just have been a tad bigger. Last 2 pics are the upstairs. Full kitchen ,bathroom, living room, bedroom, Pool Table , Bar, Washer Dryer, and a 2 tier deck. Tight but served over 50 people up there for Thanksgiving.