Well, attaching the side rooms without their own wall could just be a matter of style. But I actually agree with Dusty. The normal way to do it is to make each room with it's own wall.
Fox's house from the Graal Classic server has a good example of connecting rooms.
The joining door jams can be done with npcs like this so you can walk underneath them:
NPC Code:
if (playerenters) {
drawoverplayer;
dontblock;
}