Unit Sizing In General
A house room size can be translated to Unit Size by figuring at about one-third. If your house room size is 10x15 (150 square feet) then a 5x10 (50 square feet) unit would likely work for you. A 15x15 room would need a 10x10. Two 14x14 rooms would need a 10x15. A 3-bedroom home can generally fit in a 10x20.
Use climate control/comfort building units if you need something not to freeze or melt. This would include paintings, pictures, electronics, wine, high-value clothing, collectibles, and furniture. The next best thing is outdoor units with insulated ceilings. They are about 20 degrees cooler in summer and we have some of those also. Storing near the floor is about 20 degrees cooler than near roof, but floors can give off moisture (very normal). It is wise to put things in sealed bins and put plastic over top and underneath.