my parents house the shed is 8x12 so the same basic sq ft. they put up shelving along one side wall and the back wall to store the small/med sized stuff. the mower and other large things go inthe middle.

my shed is roughly 18x18 and most of my stuff is on shelves around the sides and my tractors sit in the middle.

if you have a riding mower, you will need to plan for room for it in the shed, then put up whatever shelves you require. don't forget to leave room onthe wall to hang/stand shovels/rakes/etc.