Most of the rooms in VF3 have different options available, and you can see them all by tapping Store, then Home Improvement, then the particular room or area that you're interested in. You can change a particular room to any of the available options, but some room upgrades are locked until your little family has reached a certain generation.

The room you mentioned (which is actually two rooms) can have a bathroom in the room on the left and a workshop in the room on the right.