The following building entrance rooms act as a shop room allowing you to place Player Shopkeepers.
Stone Shop (3 vendors)
Ice Shop (3 vendors)
Small Earth Shop (2 vendors)
Wooden Shop (1 vendor)
Underwater Shop (1 vendor)
Wooden Tavern (1 vendor)
Also the following rooms are shop type rooms:
Market (8 vendors)
Greater Workshop (5 vendors)
Lesser Workshop (3 vendors)
Shop Floor (3 vendors)
Portal Room (1 vendor)
Kitchen (1 vendor)
To add a vendor to such a room, click the Administer button at the bottom of the main screen when standing inside the room and follow the instructions on screen.