Setting out stepped cavity tray / roof abutment

[BadgerBadger]

I'm somewhat stumped!  What's best way to get a stepped cavity tray for a pitched roof abutment in the right place?

 

Our build has an attached garage with a pitched roof against the gable wall of the main house.  There is a stepped cavity tray specified along the abutment to stop water tracking down the internal wall over the garage.  I need install the stepped cavity whilst the house gable wall is being built i.e. before the garage roof is there.

 

The garage roof uses fabricated roof trusses.  My current thinking is to try and make a dummy truss/jig based on the roof truss dimensions and position this on the garage wall plate and work from there.  How is it usually done?

 

 

 

 

[Dave Jones]

ask the truss supplier for the height. find the centre mark the height and the bricky can run a string line.

[nod]

I made a dummy truss and used 450 dpc to build in 

Onsite there’s nearly always a garage truss kicking around that can be used