Building a garage over apartment?

[spacepirate]

Hey guys,

I own a small 3 bedroom home in Los Angeles and I'm zoned R2 which means I can put a second dwelling on the property. Currently I have a small 16x16 detached garage and I would love to tear it down and have a new apartment over garage built. I've seen small (approx. 600 sq ft) apartments renting around $1000-1500.

The problem I have is the math. I'm trying to get general pricing for a construction project like this so see if it's a smart investment but don't know where to start.

I currently owe 300k and during my last appraisal about 8 months ago the home was valued at $450k.

I don't really want to pay an architect 6-8k to design the thing and then find out it cost too much to build. I've tried talking with contractors and no one wants to give a generic estimate.

My main goal is to offset some of my mortgage through the rental fees.

If anyone has done something like this or has any advice I'd love to hear for you!