The windows are from http://www.kolbe-kolbe.com

I have similar trim in my house. It is lx4 on the sides . On top of the side pieces you can use a door stop which is about l/4"thick x l l/2". It overlaps by about l/2"on each side. A lx4 is on top of that. I nailed the door stop to the top piece before putting it up. I would nail a 1 x 2 to the bottom piece before nailing it up overlapping the sides by about l". I would leave a l/8" space (reveal) around the whole perimeter of the window. The top is just crown moulding (either solid or hollow. The frames I made had a lx6 for the top piece. It is a matter of what you like.

what do you mean by "door stop"? is that a type of trim?

Door stop is what I was told it was called. It's a type of trim. If they don't know what it is just tell them it is a flat piece of wood l l/2" by about l/4". They should have it.