To draw a room in SH3D you (generally) need to do two things:
1 - draw the walls
2 - insert the room to get floor and ceiling
Read the manual and in-program Help to see how this works.

If you want to add "carpeting" to the entire room, you can give the floor of the room a texture.

If you want to add a rug (or carpet) you can use one of the suggested models, or draw your own model.

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