1 building 2 gables with matching ridgelines

[Katalyst777]

It's basic geometry.

If the Ceiling Heights are the same, then you need to increase the Pitch on the two side walls to have that gable meet up with the other.

In my attached example, the pitch on the larger structure is the default 6/12, and the two side walls (indicated by wall hatching) are 8 1/2, but you might need to play around with the setting to find the right pitch for your particular plan.