Mobile homes have no foundation, so it is difficult to add a room. It may be difficult but it is not impossible. What you have to determine is which side of the mobile home will take the extra load without tipping over. There is also a chance of that you...
If you are looking to add on another room to your mobile home you can section off an area and add a door to the wall. Add the room on the other side of the door using all proper materials and tools.