[Just Got Back Into The Game] I'm just starting to play again and I had no idea how building worked (HELP)

Gameplay
6

I made a tutorial video on the builder not too long ago, he’s a link to the forum post of it if it would be of any help.

Next to that, quickly looking at your building, the red blocks mean that the hearthlings can’t reach those spots, which makes me think that those blocks reach 2 deep, instead of 1.