A 5'x10' is about the size of a walk-in closet. It can hold the contents of a mid-sized bedroom, including a queen-sized bed, a dresser, a TV, and several small to medium-sized boxes.
A 10'x10' is about the size of a standard bedroom. It can hold the contents of a two bedroom apartment, including a mattress set, bookcases, tables, dressers, sofas, and appliances.
A 10'x15' is about the size of a large bedroom. It can hold the contents of a three bedroom house, including larger items such as pianos, couches, tables, and big screen TVs.
A 10'x20' is about the size of a standard one-car garage. It can hold the contents of a multi-bedroom house, including several larger items such as a couch, refrigerator, washer/dryer, dining room set, and several large boxes.
A 10'x30' is about the size of a long one-car garage. It can hold the contents of a four or five-bedroom home including many appliances, garage items, couches, media consoles, boxes, and other items.