- Tap on a certain wall;
- Choose "Paintbrush" icon;
- Pick "Size".
Works also on MAC ("Edit" button/icon) and iOS (same "Paintbrush" icon).
On other platforms this feature will be eventually enabled.
As for now, You can change the standard 10 cm thickness by:
- adding an edited Magic Cube next to it;
- replace a regular wall by one, made of Cube.