With two triangles connect the vertices directly across (bottom to bottom etc.) from one triangle to the other with edges. Then connect a vertex of one to a different vertex of the other and so three times. This way you create triangles that should form faces. You form the shape with 6 triangles altogether. Use smooth/soften window to hide the edges you don't want to see.

@cliffordzhang said: but I need to add thickness to all surfaces as if I deposited a uniform layer of snow on the bottom and walls. But you only shared that information now? [image: mmS1_Screenshot-7_6_20188_30_54PM.png]

I don't understand what you are trying to accomplish. Can you share an image of something that looks like what you are trying to do?