Approximate Project costs
There are two ways to approach project costs at the start. Firstly, see how much you are able to afford and then work backwards to see how much space you get for your money, allowing for fees and other costs. Alternatively, you can start with the space you think you need and see how much it roughly costs - if your budget allows. At current prices, a very rough guide to overall construction costs might be as follows:
Garage conversion [say] 10-15K
Simple lean-to extension [say] 25 to 55K
Two storey extension/loft conversion [say] 40 to 80K
Major refurbishment, and/or extension [say] 50 to 130K
Rebuilding, major extension [say] 130K to 250K
Remember that the cost of certain items will depend on what you choose. The price and quality of kitchen and bathroom fittings for example can vary greatly, affecting what you can afford. Do you need to renew all your external windows or internal doors to match each other? Is your bathroom to be fully tiled? The builder will ultimately need to know as much information as possible to give you an accurate price. He will need to know if he is including these other prices within his works, or if they are to be provided by your own supplier for fitting and therefore be additional to his quote.
The final cost will depend upon the size, complexity and quality of the chosen options, noting that market place conditions and procurement methods used will ultimately determine the range of tender quotations received from different builders
The traditional formal process of inviting tenders from three potential contractors based on detailed drawings will give a range of prices allowing marketplace comparisons to be made. This process must be conducted fairly and impartially, but can be much slower and unpredictable if tenderers feel uncertain about their chances of winning the work.
If you have a good rapport with a builder you trust, you can progress an early estimate through direct negotiation with them as your 'preferred' contractor. This requires a degree of trust that the negotiated price is a true reflection of the work involved, but you and the builder will feel more engaged and the project will usually start much more quickly.