In general without an architect or contract administrator then the builder would make the valuation. On a job of this size you say comes to £5000,00 then you may say to the builder he has all the works but for ease of payment etc you would like an approximate breakdown so say you had on th figure above
2 windows to supply and fit at £1000.00
1 door to move £500 reroofing £2500 general odds and ends £1000
total above comes to the £5000
so at end of 2 weeks I would expect you to receive a valuation such as
1 window fitted £500 Doorway moved £500
25% roof done £625
Total valuation £1625
Now you only need to check if the above is correct and then you can pay him. Now what happens if you dont pay him. Well in theory the same as if he doesnt do the work. You have a contract if you agree the above and the contract is he does the work, you pay then money so if he doesnt do the work you dont pay him AND if you dont pay him he stops work. Simple, basis of all contracts. I am more than happy to workk for and to a contract as in JCT minor works or domestic works but for small jobs seems very silly to me so I typwe out a full specification plus price plus terms and you sign it. The contract is made