We are about to finish our basement in our Craftsman house. We have 1440 sq feet on the main level with 3 bedrooms and 2 full baths. The basement finishing would double the square footage. In our plan we have room for 2 legal bedrooms and a full bath. It has a separate entrance through the backyard.

In addition to the bedrooms and bath, it would have a laundry room, a utility room, a large media/rec room, a storage room, and perhaps a wine cellar. We would made the two bed/bath part into the MIL and make the larger bedroom (which is approx 270 sq ft) into the kitchenette/living and dining room.

We are debating if it makes financial sense to run plumbing and gas lines to make it a potential mother in law apartment. Do you think it is worth the additional cost to do this? Would a MIL unit be valuable for resale?