The front porch
Everybody loves a large front porch - or a large rear porch for that matter. People often think, however, that just because it's a porch it's inexpensive space to build onto a house. In fact it costs nearly as much to build as the interior finished space in a house. The reason for this is because you still have to have an engineered foundation as well as incur the cost of the roof to cover the porch. All you're missing in the end is some walls and flooring.