Break into schedules/milestones lor
. E.g. full renovation:
1) Downpayment - 10%
2) Hacking & wet work / tiling etc - 20%
3) Plumbing, WC, bath etc installation - 20%
4) Cabinet work - 20%
5) Electrical works - 10%
6) Wallpapers / painting etc all done - 10%
7) After 1 month all done & no defects - 10%
Above is just a rough guide. You can have any combination etc but make sure don't pay more for each stage than necessary otherwise they collect 20% instalment and can run away do nothing more!
Make sure they provide 1 year warranty.
However, all warranty is useless unless you get a trust-worthy ID.