Whether you choose to build or buy a sink (or anything else that's bulky), make sure it'll fit through the door, so you won't have to rebuild it should you later decide to move. Another random thought - make sure the drain system has a vent stack to a supply of adequate air volume to insure continuous flow down the drain. This can be illustrated by sipping fluid up a straw, then quickly capping the top of the straw and noting how the fluid is trapped inside the straw until it's uncapped.