I'd like to raise the roof... what am I missing?

Hello all. I’m a newbie, designing a hypothetical garage apartment. I’ve got my first floor walls (exterior and interior) done and in place, and I’d like to now create a simple gable roof. I’ve seen this done in several tutorials by drawing a line across the midway point of the building, and then using the move tool to move the two roof planes up with that line, creating the peak.

Well, I can move the line, but the planes aren’t moving with it.

I read in another post that perhaps the interior walls are some how disrupting the rectangle plane that would be becoming the roof? How would I check this?

Use the “alt” key with the move tool

actually just the move tool on its own should suffice for a simple gable, if the line is the only thing moving then it can’t be part of the raw geometry of the surface, The surface is probably part of a component or group and you have drawn the line on top, outside the component/group

You need to make sure that the roof and the walls are separate entities (by creating groups, for example). Otherwise the natural “stickiness” of elements will make operations either not work or behave unexpectedly.

What you are trying to do sounds like it involves Autofold. You might want to explore that topic to understand it better.

The simple way is to just find the center for the ridge, draw height for the slope you want, connect line to the eve edge and the you may need to also extend line over to the center so a tringle forms with a face. Then use the push pull to extrude the length of the roof.
Su often allows multiple ways to accomplish a task but do not assume what you see in tutorilas are appropriate for all cases. You could use the follow me tool but the will not get a classic Gable roof, you could make copy of it , move / copy up use yiour technique then set back down but should make it component for this case., dot dot dot.
Roof usually has over hang for rain water protection of foundation so the you could get a small line seg. at edge you will have to deal within for extrude case.