Ruben,
I see what you're up against. Especially the square window with the splayed jambs that opens up to a segmented arch head. I have to do that stuff a lot on these SoCal Tuscany McMansions (yes, the uber-wealthy are STILL building them... They're a blight; Yes, satan has a firm grip on my mortal soul).
You need to combine several methods. This will be a little bit of work.
First, place the window itself, with correct frame, sash, mullions, etc. Assign a marker and ID to it for specification / scheduling purposes.
Next, use the splayed opening object. Make it to fit over the window. Slide it in place. There's nothing stopping you from placing two opening objects on top of each other. Turn off it's marker and assign an ID that will be ignored in your schedule element.
Finally, make a mesh on the floor plan that creates a 'cut body' to use in an SEO to form the tapered, splayed arch. Save it as a GDL. Hack the GDL code to rotate it to the proper orientation, then slide it in place. Do the SEO, then put the 'cut body' object on a layer that stays turned off (mine is called "U-SHAP"... That means 'Utility' and Shape')
The splayed opening object will make your opening display properly on the floor plan. The 'cut body' mesh with the SEO makes everything look proper in elevation, section and 3D.
If you have to edit this assemblage, then it will be a bit of a pain, but it will be RIGHT. I've been paid more to DRAW a window than it cost to BUY the window at least once, I'm sure!
Other tips: Tell the mesh you want all it's ridges smooth. When you write it to a GDL, add MUL codes to the 3D Script so you can re-size it if necessary... if it only needs a few cm change, it'll still look fine. In the 2D script, just use the PROJECT2 3,270,2 command. You'll have the object's layer turned off normally, so it's okay if it's ugly in 2D. Finally, be sure and make it's material controllable so you can match the window jamb's material; it may seem ridiculous, but trust me... just do it. You'll be happy later.
Save the object someplace outside the project, with your other custom objects. You'll use it again.
Hope that helps.
Give me cute or give me death!.... I live in Orange County.