Ask if the builder has NVQ or HND qualifications in construction and see copies of certificates. You could also contact a trade association to see which qualifications are relevant to the type of work being done. If you're having electrical or gas work done, you will need specially qualified people to meet safety standards. Professional associations can often help you find qualified people in your area.
Check that the builder has insurance cover and that it won’t run out while they are working. The builder should have public liability insurance which is needed in case someone gets hurt on site. They may also have cover in case there is damage to your property, they go bust or have an accident, so you can pay someone else to finish the job.
Before you start any major building work, contact your local authority planning department to get planning permission. If you don't get planning permission where needed, you'll be breaking the law and you may be required to pull the building work down.
Some building jobs need to meet building regulations. To ensure the regulations are met, you will either need to use a tradesperson registered with the competent persons scheme in England and Wales or a tradesperson who is an approved certifier under one of the Scottish Government’s building certification schemes in Scotland, or involve your local authority Building Control Department.
If in doubt, get advice from your local authority.
In England, the government leaflet Building work, replacements and repairs to your home tells you more about the competent person scheme and whether the work you're having done needs to meet Building regulations. Go to: www.gov.uk.
You may need to use a surveyor, architect or quantity surveyor if you are doing work that:
For example, an architect can draw up plans to submit to the local authority. You can get advice on whether you need a surveyor, architect or quantity surveyor from the Chartered Surveyor's Voluntary Scheme or organisations that represent surveyors and architects.
If it's a large or complicated job, make sure you get something in writing. This could be a contract, a letter of agreement or a written quotation.