Placing a 100 gallon commercial water heater on a roof top is tricky. Especially on a 6 story building. You'll need at least one person who is certified in rigging. For plumbers it's best to hire a crane and rigging company to make the lift safely.
Most homes in Northern California have natural gas service. The provider is Pacific Gas & Electric (PG&E). What homeowners are responisble for is simple. That is, all property owners are responsible for installing and maintaining all piping after the PG&E meter. But here's an exception. Currently, PG&E is busy installing and uprgrading a large amount of their underground (UG) delivery mains. At times that will require moving the meter on your property for safety concerns. PG&E may dictate that your meter requires relocation. This will require repiping the part that you own, so it will route to the new meter locaiton. Here's the good news; when PG&E dictates a meter move, they pay for your piping to be re-routed. For that part PG&E will use and pay for a plumbing contractor to move your line. PG&E is concerned about the safety on their natural gas delivery system, and they're doing something about it.
The strainer is your first line of defense for keeping your drains clog free. A large majority of residential drain clogs are due to hair getting into the drain. The stainer, as pictured here, will do a pretty good job of capturing the hair before it enters the drain. These strainers. for tubs and showers can be purchased for around a $1 at your local hardware store. Even cheaper, your plumber will likely have a few laying around in his/her van. If you ask, he or she will likely give you one for free. A cheap investment that prevents having to clear the drain. If you do need to clear the drain, see our plumbing tip blog from November 11th, 2014, "shower drain cleaning made easy"