Like Jason said, build one tall enough(just a couple feet more) so you can put an overhead floor for storage. I did it. Even put in some attic pull down stairs to access it. It is more for permanent storage for boxes, etc. as by the time you start filling up the bottom with lawn mowers, etc. there isn't much storage room. I built one 10'by16' with standard 8' side walls before the barn roof started. Left the 2 front upper joists open with a deck type railing on the upper part in case I wanted to slide some long stuff such as lumber into the over head area. A cheap octagonal window at each gable end made with plexiglass and framed in has a nice and cheap effect as well as letting in some light. Next I'll run electric out there and put in a subpanel for lights. I've filled up both levels of the 10by16 and wish it was bigger now.