I went 25' x 36' on the inside to meet HOA rules, I had to be at 900 sq ft or less for no town meeting variance, and I only have 5/8 of an acre with a 1600 sq ft house.
I made this 900 sq ft size work to fit all my toys and still have room to work.
2 cars, 1 truck, 1 boat, 1 motorcycle, 50"...