This post gives a brief outline of what to look for when it comes to buying materials and managing property refurbishment.
You should, first off, know what a good price is for the items that you wish to buy. Get the following trade catalogues:
You can compare what sort of prices these three companies are charging and use them as your benchmark. A lot of builders usually end up going to these suppliers (smaller merchants would often charge more due to not benefiting from economies of scale) so you can know whether the materials quote they are giving you is over-inflated. Labour costs vary according to location, time of year and the job itself but you can get a general feel by phoning around a few builders using websites such as Yell and asking what their day rate is.
Some other useful websites: