As with any profession, it is very difficult to say precisely what makes a good contractor. It’s something close to a combination of attention to detail and reliability. There is no such thing as the right amount to pay: you will have to judge whether the tradesmen are worth what they are quoting. Make a note of the builders you approach and the estimates they give you for the work. Always check the quality of their past work with previous clients.

I hope that Price the Job will help you to clear the fog surrounding general building work that you might want to do on your home, enabling you to be in control. One of the most important things, when planning building work, is to make sure that you have enough money for the whole job. Don’t get carried away buying expensive fixtures and fittings unless you are sure you can afford them. It is wise to ensure you can fund an extra 10-20 per cent of the costs in case unforeseen problems arise.

THE BUILDER

“Builder” is a convenient catch-all term that covers everything from a main contractor to an odd-job man. Because most builders are VAT-registered, you will have to pay an additional 17.5 per cent. If you are a domestic customer, you cannot reclaim VAT so you have no choice but to pay VAT on all labour and materials.

Main contractor: Hiring a big main contractor to carry out all the work on your property has the advantage of providing an in-built project manager. He will take the responsibility for everything to do with the job, however big or small. He will organise materials, sub-contractors, building inspectors’ visits, and liaise with your architect if you employ one. Generally, a main contractor has more than one job on the go at a time, so he will be juggling to make sure his workers are constantly employed. The contractor is responsible for the quality of the work of his sub-contractors, so if anything goes wrong he should deal with it. To cover overheads, hiring a contractor is likely to put a mark-up of at least 15 per cent on the cost of the work.

Sub-contractor: If you are determined to shoulder the project management yourself, you will be using specialist sub-contractors or individual tradesmen. Specialist companies cover a specific trade and employ several people skilled in that trade. Again they will put a mark-up of at least 15 per cent on the basic price of the work. It is still advisable to go by personal recommendation or to follow up references given by previous clients.

Small contractors: They can supply different tradesmen but will not take on the full responsibility of a main contractor. They may well leave building regulations, the architect’s drawings, ordering materials and such like to you. Very often builders who are small contractors will have a specialist trade of their own, such as plumbing or electrical work, but they will bring in other tradesmen as required.

The odd-job man: This can be the cheapest option, as his overheads should be lower than those of any company or contractor. On smaller jobs he will be able to do the work of many tradesmen. For example, if it’s just a simple job such as patching in a bit of blown plaster, he may also be able to fit new skirting and to decorate. The decision will have to be made between paying a day rate or a fixed price.

COWBOY ALERT

The surest way to avoid falling victim to a cowboy is to follow personal recommendation, so start by asking friends and neighbours. If that fails, try a trade association for members in your area. The Federation of Master Builders runs a great website: www.findabuilder.co.uk.

GOOD BOSS/BAD BOSS

For every cowboy there is a potentially bad employer. To get the best from your builder, make sure you are not one of them. Be prepared to brief your builder precisely in writing about the job; agree a price for the job and the stages at which you will be paying; pay up accordingly; try not to change your mind halfway through; expect to pay for any modifications to the original plan; and let him get on with the work without distractions from you. Agree whether he will be removing all building rubbish at the end of each day or at the end of the job.

GETTING QUOTES

Select three contractors and ask them to give you a written quote for the work. Also ask for three references and follow them up, asking previous employers whether they were happy with the job; if possible, look at the quality of their workmanship yourself. It’s wise to do all this even if they come with the highest recommendation. Check their insurance cover by asking to see their builder’s liability insurance certificate.

THE AGREEMENT

Once you have chosen your contractor and have decided on the way ahead, make a written agreement that specifies the work to be done in as much detail as possible, right down to the clearing away of rubbish. The agreement should name the negotiated price, including VAT, and the payment stages. Be cautious about paying for anything in advance — including a deposit. The contract should set a start and completion date with penalty clauses if the work runs over. It should stipulate any special instructions, including how to deal with those inevitable extras. Both parties must agree how much it will cost and both must sign the agreement. Extras should crop up only if an unforeseen problem arises or simply because you change your mind.

It is easy to rack up large sums without realising, so make it clear that any extra costs should be agreed before additional work is carried out. This way no dispute should arise.

Reader offer: Get Sarah Beeny’s Price the Job, published by Collins and Brown, for £7.99 (RRP £9.99) with free UK p&p. Please call 0870 7871613 and use reference CH545. Offer ends on April 15.

Times recommends

• Second homes: credit crunch casualty or money-spinner?
• How I built my own sliding house
• Top 10 incentives for house buyers