Usually any time you order an arched top window of any kind, you can get it with pre-made trim for that window. Go back to the manufacturer and see if you can get the trim you want. As for the exterior trim, I'm confused on your question. When you speak of trim, do you mean the 2" wood brickmould that goes around most wood windows or do you have an aluminum clad window with a nail fin? If your replacing an existing window that used to have a wooden brickmould with an aluminum clad window with nail fin, your exterior void where the old brickmould was located must be custom bent on a brake and capped off. It is done by piecing to get the arch. Unfortunately this is the only way to do it. A good skilled installer can do this fairly easily. Otherwise a wood window should come with brickmould already attached to the exterior side. Hope this was in the right direction for you!

As a followup, I chose the 1.5" (as I guess I could always replace it with wider in the future by just cutting away more siding). However, now that it is in, it looks a little odd. Not necessarily the width, but the depth. It was only 1" deep (they said 5/4"). But when it's in place, the window frame protrudes more than the trim. It's just a plain trim, so perhaps that's normal (since usually, I see either wider trim that I think is often flush or some sort of brick molding that I guess is meant to stick out more than the frame?) Anyway, just wondering if this (trim recessed more than frame) is common. Thanks

You might also want to ask your contractor if the housewrap is being installed as required, because that’s a BIG deal. Per DuPont: “Water-Resistive Barrier (WRB) Code Requirements The 2015 International Residential Code (Section R703.1.1 Water Resistance) requires that “the exterior wall envelope shall be designed and constructed in a manner that prevents the accumulation of water within the wall assembly by providing a water- resistant barrier behind the exterior veneer as required by Section R703.2 and a means of draining to the exterior water that enters the assembly.” Section R703.2 (Water- resistive barrier) states that “one layer of No. 15 asphalt felt, free from holes and breaks, complying with ASTM D 226 for Type 1 felt or other approved water-resistive barrier shall be applied over studs or sheathing of all exterior walls. Such felt or material shall be applied horizontally, with the upper layer lapped over the lower layer not less than 2 inches (51 mm). Where joints occur, felt shall be lapped not less than 6 inches (152 mm). The felt or other approved material shall be continuous to the top of walls and terminated at penetrations and building appendages in a manner to meet the requirements of the exterior wall envelope as described in Section R703.1.”” FWIW: Whoever cut and laid the stone did do a nice job; it looks like a much better job than what was done by the dingbats who built my house!

Thanks for the input, everyone. Irene - thank you for sharing the pic. I fell in love with the trim and that's what we're going with. Elizabeth- once you mentioned too modern not to have casing, I looked at it from that viewpoint and I agree. Girl: the reason for deep sill is probably an added layer of insulation, as is the case with my room. Ours is a split-level ranch, and this new bedroom was previously a double integral garage. The windows are where the garage doors used to be. Once we studded out the walls and added a thick layer of insulation, the result is these deep set windows. I personally love it because any extra space for more plants is a plus in my book! This reno allowed us to create a large 4th bedroom, and a nice size mudroom/laundry room on the other side of the bedroom wall. I'm very excited :)