I would make the panels with the slab tool, and make a larger, simplified underlying structure out of just a few walls. I suppose you could also try using the curtain wall tool, but I would need to play with that one a bit. Maybe someone else has more ideas on that?
You can make irregular window holes by using solid element operations and the beam tool, with the beams being on an invisible layer. They will cut a hole through the wall (but not a panel overlying the wall).
You can also create your own window shapes with just a bit of GDL. Reference the Building Objects Creation interactive training guide from Graphisoft.com.