How to build multi-level rooms in Stranded: Alien Dawn. A little tutorial how to build fully-closed multi-level rooms with indoor stairs. The tutorial includes detailed step-by-step instructions with screenshots.
Step-by-step instructions
The main trick is to place a roof over the bottom part of planned stairs before placing the stairs, and to place a roof over the upper part of the stairs after placing the stairs.
1. Place foundations but keep empty blocks for stairs
2. Place roof over the lower room
3. Place stairs, their top platforms fit the empty blocks
4. Place roof over the upper room
5. Place walls around rooms and where rooms connect 
6. Done, multi-level rooms are fully closed
7. Optionally, you can add a wall, and… 
8. … place doors or doorways