A good bit of starting advice might be 'measure twice, cut once'!
If they're using made up angles and bends then it's a piece of p and little more than measure up, cut to length, offer up, mark up, drill out, sling it up, bolt together.
If he's manufacturing bends then get a gook bood on tinsmithing or sheet metalwork perhaps?
Useful/necessary to have in the toolbox;
* Quality PPE, goggles, gloves, coveralls that don't burn too easily
* Quality 4.5" Angle Grinder with carb cutting discs, grinding discs and Emery wheels (plenty of each, dry stored and fitted properly!) If you can manage two it often saves time swapping discs or thinking too far ahead to save changing discs.
* Quality Power drill (HSS and masonry bits) pref with hammer
* 2nd Cut (or b-astard) half round file (for dressing edges)
* Combi Square (for measuring angles)
* 5m steel tape
* Dividers (for marking up)
* Another pair of hands :O)
Some timber for laying tray on for cutting, one piece either side of the cut and enough to support any bits hanging over to keep the job flat.
Probably plenty more to add but it's early! Hope that's a useful start