Minecraft wiki entry for Shelters, associated text: A mountain hideout
A floating house
A small dirt shack (Good for the first night)
Small one or two story house
Large 2 or 3 story house
A hill fort
A treehouse
An underground shelter
A small fort
A larger fort or castle (a collection of buildings, sometimes arranged around a courtyard. Usually with defenses)
A walled off area (Even if there is no ceiling, it will still let you sleep if it's closed off)
A very large castle (about 40×40×23)
A mansion (Bigger than 30×30×10)
A cabin
A dugout (When making it, you will gain and not use blocks, unless you run into an opening that you want to block off.)
An underwater base (not a good first shelter.)