Keep Records. No, Really Detailed Ones..
No matter the size of your project, before long you'll need to match a tile, a paint colour or try a warranty claim on on something you bought in the madness that is doing a build project and you'll wish you had done this!
- Write the ID details and supplier on a sample of every tile type you use and snap a picture with the receipt and a note of where they are installed.
After first fit electrics, before the wiring is hidden away, take a picture of every wall in every room so you can avoid damaging cables in the future.
Even when you've just taken delivery of the paint, write the name and colour code etc on the plastic bucket with a permanent marker. The labels fade as fast as Thai receipts (and that means in no time).
A copy of the building plan with the paint and tiles used is invaluable. Don't forget the outside too.