Trimming and joining 2 surfaces

Morning guys!

I'm trying to simplify my 3D model so that I could run an analysis on it via finite element (GSA).

I have 2 separate shell surfaces (shell 1 - Roof and shell 2 - supporting structure) where I would like to trim shell 2 so that it would shell 1 as illustrated in the sketch below.

Initially I was thinking of extending the top portion of shell 1 (dotted lines on sectional view) and trimming the excess where it crosses shell 1.

Would appreciate some guidance if there is a better approach on this. Thanks a bunch!

Shell 1 - roof (in yellow), Shell 2 - structure body (in black)

Side view

Plan view

Sectional view