Fitting a door and a window

[SaladFingers]

I need to fit a door and a window into my garage. Going composite/pvc.

Can anyone give me some guidance for fitting these? I've never done it before, but can imagine I'd need someone to help me hold things in place. I know I'll need to use levels and packers etc, but just haven't done it before, so I'm not bristling with confidence, but am quite competent with things really, but thought I ought to seek some advice first. Ta.

 

[foxhole]

Make sure you do not distort the frame when securing , pvc is very intolerant , door binds easily if not square and level.