Steel kits you can order and install from plans. You could utilize some of the raised center aisle barn kits from one the companies selling carports etc. The carport companies are everywhere here. The build on site prefab shed buildings are also. I subbed a custom for one of them a few years ago. Bad bad deal, would highly discourage anyone from doing it.
But their general idea is solid for a small storage building.
Local codes need to be addressed and any other obstacles that govern freedom of land ownership. I would suggest looking a some of the plans in the books for shops and barns. Box stores have several. Kits are going to be stripped down to save every penny. More accountants involved than engineers. I built a shop for a big hunting club and used prefab steel trusses. They were sq tube with brackets for two by's purlins. I really liked how they worked. 6x6 treated posts 2x6 lathing 26 ga residential metal. I have pictures and will try to post them. My shop is oil field pipe, scrap purlins, salvage I and h beam and what was handy. Still has the original dirt floor! I would just do some looking for what works with your plan and budget. You never hear anyone say their shop is too big.
