backyard/sideyard storage shed

[Jim G.]

Want to build a sideyard storage shed. The SFH is located in Northern CA Bay Area. ideal size would be 8'x18'. Need to be insulated and may have windows and door (rolling garage type of door is ideal). Can I use prebuilt garden shed such as Tuff Shed? Tuff Sheds usually come with un-insulated. Can I add insulation?
My think is that I can use shed to store landlord stuff (not as rental) and rent out rest of house.