Shop around. You may be able to rent some commercial space. Lots available in my town. If you grow--rent a bigger place.
What are the pesticide requirements in your state? Special storage? Rinse pad? Containment? Locks? Lighting? Ventilation? No floor drain?
Fertilizer attracts a lot of moisture from the air in hot weather. I am not sure there is a way to prevent this--short of AC, but consider humidity. Do you need to store grass seed? Plan to wash inside? Need to prevent freezing of chemicals or pumps? Do you plan on pallet racks for storage? Loading ramp? Truck dock? Lift truck? Do you need a place to attach a chainfall for hoisting? Can you remove skid sprayer easily? Lift your plows? If you have water in building--employee bathroom and shower, breakroom, drinking fountain and a means to fill tanks--then do you need to prevent freezing? If you store pine straw is it a fire hazard? Will chemical odors be a problem? Do you plan to paint equipment in the winter? (Not too cold, odor and fire hazard).