As A baseline, these guys will build you a no options unpainted 16x24 for $12099. Add on cost of paint, upgrades to make it fit in better with your existing house, and some driveway work to get to the building, and I suspect you will find yourself somewhere around $15-16k. If your HOA would approve a metal building that doesn't look anthing like your house, you could do it for around $7k.