Should I buy a garage or work in garage under house

From personal experiences: DO NOT do this if you have a gas water heater.
Fumes will creep along floors and ceilings to a pilot light. One fuel leak or paint/primer session can get REALLY dangerous.

I install tank- less electric water heaters in my house for this reason. (Plus it frees up garage space).

I have worked in three different motorcycle shops that had fires in their pasts due to this.