The cost of a room addition depends on the size of the room addition and your location and who you hire to do the room addition.
If you can build the room addition yourself then you might be able to do the room addition for around $3,000.00 to $5,000.00
If you hire a contractor to add the room addition it can cost you $10,000.00 to $15,000.00 depending on the size of the room addition and how fancy you want the room addition to be.
If you have a bathroom added onto the room addition then the cost can go up.
Having a room addition added onto your home can also increase the value of your home so you can usually get the money back and more if you do a room addition.