Alkyone

Well realistically you need to have a garage to perform most of your work. I know there are garages that are self service, you pull in, pay very low fee to loan equipment and rent a bay and bring your own parts, do your own work and leave. But that'd still require you to RP it out arranging it with the garage and the like. If you insist that your house is simply fully equipped with everything to do body kit change and engine customization - then virtually everyone can RP that about themselves making garage wholly pointless. As to police camping a parking lot - I see no issues with that. If a spot has recurrent criminal activity (and the garage kinda does see a lot of suspicious activity pass), then seems logical for the police to watch the surroundings. Nothing stops you from asking the officer to move to another spot that isn't reserved for clients if you feel it necesarry.