A facade with windows is to be modelled for an outdoor view. The windows are half-rounded. 

The frames on the outside and the window sill are to be taken into account too. 

The following image shows one possible way of doing this. Use is made of nested Boolean groups in order to implement the final result. 

On the inside, this is a union (wall with frames and their window sills). Holes for the window openings are subtracted from these.

Example of modelling a facade

Modelling the wall and an individual window frame.

Rectangular cuboid for the wall.

Rectangular cuboid for the window sill (blue).

Rectangular cuboid for the window frame at the side (green).

Round cuboid for the window frame at the top (blue). Convert into a polygonal cuboid and scale in the y direction. 

Delete the superfluous points at the bottom.

Group together the cuboids for the window frame and the window sill in a free group and duplicate as a field (5x5).

Form the Boolean union between the wall and the group (window frame and window sills).

Generate the same cuboids again as those that were modelled for the window frames under Point "1" above, but without the window sill. 

This time, however, reduced by twice the thickness of the window frame (for the window cut-out).

Group together the cuboids generated under Point "4" above in a free group and duplicate as a field (5x5) – window cut-outs.

Generate the Boolean difference between the union generated under Point "3" above and the window cut-outs (Point "5").