I see another terrorist attack (hope this doesn't happen) on the U.S. soil bigger then 9/11. 

. -- although even if you are in HPOZ, there's very little they can legally do to stop you do an ADU, especially if you aren't doing any substantial demolition, and there are ways around some of the hillside restrictions depending on where you are)Cost- It will depend on the condition of your garage's structure (footings, slab, wall framing, roof framing), the distance that's required for trenching, any electrical panel upgrades or location changes, and your design intent- Check that your garage has footings that are deep enough below grade (12" min in LA City, 18"-24" elsewhere) -- if not, you'll need to underpin or rebuild them- Check that you have concrete curbs, as these will help stop water intrusion from adjacent soil -- if not, you will want to find a way to add them, either by making the contractor do surgery on the building, or by adding them as part of a larger demo+rebuild strategy for the entire garage- Look at your slab.

After lifting one corner of the carpet, I realized that there were beautiful hardwoods underneath, which is obviously a selling point.