Each requirement, or group of requirements, in your specification should be priced. Against a taut specification, a contractor can supply a reliable quotation, which will appear in the first section of your pricing spreadsheet. such spreadsheet usually has 4 sections: price for contractors work, price for furnishings and fittings, professional fees and risk provision. These 4 sections should give you the total cost of your project. The spreadsheet will help you to manage your figures and to see where you might trade one price for another.
For higher value projects, a competitive tender should help you to obtain better value for money. When choosing your contractor, make sure you are comparing like with like. The more detailed your specification, the more likely you are to obtain a true comparison of prices.
Remember to agree the price with the contractor for any additional work before committing to it and keep an eye on the overall budget. Hopefully, if the risks dont materialise, you will have a sum available to spend on these further tasks. You need to watch that the cost of house renovation doesnt increase disproportionately as a result of additional work. Contractors know that you have few alternatives. So, when checking references, ask previous clients specifically whether the contractor priced additional work reasonably.
Pricing spreadsheet: a key element in controlling your renovation spendings.