House levels ad walls up/down not working.

Hey guys, apologies if this has been posted before.

I'm in the process of building a large new house on a lot I cleared. Everyting is ok in build mode, but when I switch to live mode with a Sim in the lot, I can't move the camera up and down the house levels (with the arrows in the top right) or take the walls out of view. All I can see is the entire exterior of the house with the walls up. To see inside I have to push the camera through the walls. Any idea how to fix this?