Basements are a rarity in the markets I frequent here in CA.An observation from this forum, many contractors and experienced REI have advised against finishing basements because of low ROI and the comments "it's not if a basement has water intrusion it's when"

The list for new builds can be a lot trickier (poor construction/ construction defects, new materials being used that haven't stood the test of time yet, foundation issues from expansive soils or bad concrete being used (harder to know because the damage isn't visible yet), sewer line might be already jacked up or done wrong, windows or roof may not have been flashed properly but water damage isn't visible yet (I've seen new builds where you could literally see daylight coming in through gaps around the windows), grading or drainage issues, truss rise, nail pops, water intrusion, cheap appliances only made to last a few years or poorly installed, dirty ducts from registers not being covered during construction, wood shrinkage cracking the sheetrock, doorframes off/sticking doors and windows, apparently mold and meth may be present already... both old and new require due diligence and an experienced inspector. 

After about the 3rd worthless intrusion,  all your tenants will feel this way. 

Much less intrusive into every penny you have.

Water intrusion, settlement, drainage backup, pests, radon? 

We had to deal with Covid, water intrusions in basements and roofs, feisty neighbors, a quasi squater in a shed. 

That's different from an issue with actual water intrusion into the brick, which will delaminate paint from brick for sure but is a structural issue that should be corrected.

There's no limit, but the Landlord should be respectful of their right to quiet enjoyment and keep the intrusions to a minimum.

. -- 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.

These are the following Repair or Replace recommendations from the Inspector:Concrete Stepsfascia around the perimeterclogged drain or flooding potential by drivewaysigns of water intrusion noted in the basementaging signs on room (Potato chip constancy)cracked shinglesNo metal chimney capChimney flashing leakingdrywall cracking in Living room of unit 2Flooring in Kitchen unit 3 is damagedThe ignitor for the oven in unit 4 requires replacement.The toilet in the bathroom of unit 2 is leaking.