3 way vault from a set perimeter

I want to create vault that starts from the perimeter I set, with 3 rectangular openings.

When I do Normal style lofting, I get these wings on the top.

When I do loose, it escapes the perimeter, and create the triangular hole on the top.

Any will be greatly appreciated!!

Hi @ferhyunt
I’d probably go Sub-D for something like this.

HTH, Jakob