So I asked for help about something similar but now, im trying to make the building in the rock and I can’t get to know why it’s always red! It’s seriously starting to make me crazy :c Please tell me there is a way to make it…
Umm i see, the problem is that they cannot build the roof ir the upper things, because they build this from the top and they cannot do It from down, then you have to delete that and later you try ti build It again
yeah, I’m pretty sure @juan_david_giraldo has it spot on. To clarify: hearthlings build roofs by standing on top of them, so if there’s any blocks that need to be built underneath the natural ceiling from the rock formation then the hearthlings won’t be able to “reach” them.
My advice would be to use the slice tool layer by layer (the small/single arrow rather than the one for 5 levels at a time) to check that there’s
a) no blocks underneath natural terrain blocks (need 3 blocks’ tall space so hearthlings can fit)
b) no blocks or windows etc. stuck into the walls by accident
c) sometimes hearthlings try to build walls from the “outside”, particularly if they’re built on top of a newly laid floor. If the game decides to build this way, then again, the hearthlings won’t be able to stand in their preferred spot “next to” the wall if there’s solid rock in the way. The easiest way to get around this one is to build the walls separately rather than as a full building – then there’s no “inside” and “outside” during construction, and hearthlings will have a better chance to just stand wherever they fit.
There are a lot of reported issues when trying to build inside terrain like this, so my advice would be to break the building down into individual walls/floors/ceilings/etc. as separate templates. It may take a lot longer, but you’ll have a lot more control over what gets built when, so you can guarantee access to wherever it’s needed. If something still refuses to be built, you can open the command console (ctrl key + C key), select the building, and use the command “ib” to insta-build the offending part. Building one-wall-at-a-time is a great way to watch and learn how the hearthlings go about their building jobs, too – so it may help you figure out designs that work nicely even inside caves/carved out areas like this 
Thank you all for the help, ill try all of that. Is there going to be an update to make things easier?
only if a mod gets made that alters the way buildings are build
does’t have to be easy al the time 