I have had 2 in Colo at 2 different houses.
1)1st was built in a gully by PO that became a river every spring. nice big 30x40 bran shitty location..lesson learned check out your area well
2) I built one my self at current house 20x40 with overhangs on both side to park stuff under... lesson learned build it bigger ( you will have more $$ latter) I poured the floor ( nonweight bearing latter, that way is an ag building per local building code) I pulled a permit when I wired it and they never asked about the building ( ag)
make it wider / bigger 20 may be 2 car garage with but not wide enough when you are working on vehicle project to park another vehicle