1. Plumbing. Residential plumbing typically uses 1½-inch pipes for drains. You’d be surprised how much gunk and hair goes down that drain. The larger the drain, the less likely it is to clog. The cost difference to upgrade to a 2-inch drain is practically negligible, and unless your framing doesn’t allow for it, you should consider increasing the drain in your shower to 2 inches.
Also, If you live in a region where temperatures drop below freezing during the winter, it’s important that your water supply lines don’t get routed through an exterior wall.