"A" frame 1st floor

[Old_Timer]

Hi all,
Anyone know how to make an "A" frame wall for a beach house which will accept a central window?
I've tried geometric shapes such as wedges etc and a small rectangular wall as the core "in which the window is fitted" all of this works but when applying the final texture all the joins show up where geometric shape or slab meets wall etc no matter how accurately they are placed.

See screenshot for better detail of what I'm trying to achieve.

Cheers