Improving on the parts located at http://www.thingiverse.com/thing:2998...
I have printed multiple parts together (combo files) and the gaps are so small that the parts are joined together during printing. I think they could be broken apart, but I like them joined.
I will upload a zip file of the parts in STEP format so people can easily modify the designs. For example, you could combine different pieces and then print them all at once to save time and make the whole thing a little more sturdy. I have stl files of three combination pieces included. (2x2_combo_straight, 2x2_combo_doorway, and floor_2x2)
More parts as they become available.
Print whichever pieces you want. The floor pieces hold the wall pieces down. For large areas of floor, there might be some small gaps depending on which floor tiles you use.
For the door, I use a piece of paperclip as a hinge pin. If you have a drill the correct size, drill a hole in the doorway and the door to match. If not, I just use wire cutters on a straight piece of paperclip and leave the "bit" in the hole when finished.