Aluminium doors and Windows from China for Double Brick house in WA

Hi, I'm an owner-builder looking for some guidance on ordering aluminium windows and doors from China.

I'm trying to understand how to determine the exact measurements from the engineering drawings. If anyone has experience with this process, could you please advise:

• Do the windows and frames typically come as a complete unit, or are they supplied separately?
• Are there any bricklayers or installers you would recommend who have experience installing imported aluminium windows and doors?
• For internal doors, what is the best way to measure accurately so that everything fits correctly when the doors arrive in Australia? I'm hoping to avoid having to hire a carpenter to modify or resize them.

Any tips, lessons learned, or recommendations from people who have gone through this process would be greatly appreciated.

Thank you.