Thicken stair object with Booleans

- We need to thicken this stair,…so that it can be build -able.…I'm going to zoom in here, and make sure that…dynamic UCS mode is on,…and then type PL for polyline.…Enter.…Position the cursor over this surface,…and the dynamic UCS feature will automatically reorient…the coordinate system, so that the…xy-plane is parallel for this space.…Then draw your polyline from this corner…and turn off ortho by pressing f8.…

Navigate to the top of the stair,…and snap the other end of the polyline here,…to this endpoint.…Then toggle ortho on, move the cursor down,…type one foot, enter.…Toggle ortho off.…Navigate down here, snap that polyline to the intersection…point, here, on the end of this tread.…And then type 'c' for close.…So now we have a closed polyline in the correct plane.…

However, if you look closely, you'll see that we have…little triangular gaps between this polyline…and the existing stairs.…We need to do is fill in those little gaps by copying…some of the stairs.…I'll use the copy command, and select each…one of these stairs, not including…