10 x 15 typically fits a medium sized apartment in ins entirety or three average bedrooms' worth of furniture.

10 x 20 is comparable to a standard one car garage. This size typically fits a small house or multi-bedroom apartment in its entirety, otherwise furniture from a kitchen, living room and two average bedrooms. 

10 x 25 is comparable to a large one car garage. This typically fits a car comfortably or furniture from a medium sized home in its entirety.