By Zoe Dare Hall

After two decades spent building up a property portfolio of more than 700 buy-to-let properties and becoming two of Britain's most successful landlords, the time has come for former maths teachers Fergus and Judith Wilson to sell.

"Old age, dear," explains Fergus, 61, of his motivation to rid himself and his 59-year-old wife of their £180 million portfolio at a time when most British buy-to-let investors are only just starting to see hope again.

The seed for their property empire was planted in 1986, when Fergus and Judith realised that in order to move to a larger family house, they could keep their existing home and rent it out. The new mortgage cost them £10 a week more than the rent, which seemed a cheap way to own a second property. "But I knew if we grew, we couldn't afford to lose £10 a week on every property," says Fergus, so in 1991 they began buying tenanted properties at rock bottom prices. The rent covered their outgoings and the capital values rose in the mid-Nineties, so they would remortgage and reinvest.

They have received requests to buy anything from one to 100 of their properties, but they are looking for someone to take over the entire stock. "We are looking for vacant possession prices, which are going up by on average £1,000 a month per property. But the buyer will get the benefit of not having to find tenants, as every one of our properties is rented out," Fergus says.

Fergus is keen to impart his knowledge to others thinking of becoming landlords. "It's a matter of when you step on and step off," he says. "The property market… follows a linear progression and, if you follow common sense, property of the right sort will always go up in value."

So here is buy-to-let common sense the Wilson way.

1 You are in the business to make money, not to help people

Property is an investment and a commodity. Don't get emotionally involved with your tenants. "You may have to reject them if they don't have the deposit or a guarantor. Don't let your heart rule your mind," says Fergus. Decide whether you are a professional landlord looking to earn income from your rent, or – as most people are, including the Wilsons – a property investor expecting the rent to cover the outgoings while the house rises in value.

2 Buy two or three-bedroom houses – and never flats

Except if you're in London, where flats will be in greater demand than in suburban areas. "One-bedroom starter homes are no good as people want to move on within six months," Fergus says. There is also limited demand for four-bedroom houses. "Why would anyone pay £1,300 a month in rent when they could get a mortgage for less?" he asks. "Rock-bottom rates have shifted the balance, but generally it should be cheaper to rent than buy."

3 Buy new or nearly new

Avoid the cost and time spent doing DIY. "You don't want the hassle of having to fit a new bathroom and kitchen. Most people with about £200,000 to spend are older and not the DIY type," Fergus says. New-build properties have the added benefit of a NHBC warranty, boiler guarantees, double glazing and tend to attract more professional tenants.

4 Choose your tenants carefully

"I had no trouble [with tenants] for 19 years, then four people inviting me to a punch-up in a year – luckily I'm a big man," says Fergus, a former rugby prop-forward. "You'll see all sorts if you do it as long as we have, but generally it's a bed of roses."

Do checks to ensure they are creditworthy and have a guarantor who is a home-owner. And the best tenants? "Middle age couples who have recently got together from previous relationships," Fergus says. "They won't be moving for promotion so are likely to stay a long time."

5 Leverage your money

If you have £200,000 to invest, don't buy one £200,000 property, buy two and put £100,000 down on each house, says Fergus. He then recommends getting a 50 per cent interest-only mortgage on each. "If you can find interest rates under five per cent, the rent will cover your outgoings," he says.

6 Magnolia wins every time

"Don't impose your tastes on others by painting your house lots of colours. Stick to bread and butter houses. A two-bedroom mid-terrace house painted in magnolia and white is what most people want to rent," Fergus says.

7 Avoid ex-council houses or bungalows

"In ex-council houses, rents will be lower as you will only get as much as the rents office will pay. Ask yourself: 'Who will want to buy it?' " Fergus says. "[With bungalows] you can pay 65 per cent more and receive only 15 per cent more rent than you would for a two or three-bedroom house on the same size plot."

8 Buy close to home

All of the Wilsons' properties are within 30 miles of their home, mainly concentrated on new-build estates in Maidstone, Ashford and Hawkinge. "Go for an area such as the M20 corridor, where there is rental demand and rising prices. The prices of our houses returned to July 2008 levels by July 2009 and have risen since," Fergus says. Don't, on the other hand, buy in an area with a big retirement community. "You don't want economically inactive tenants."

9 No smokers or mechanics – but dog owners welcome

These are personal preferences of the Wilsons, "but generally dog and cat owners tend to keep the house in better condition as they are always hoovering up the hair," Fergus says.

10 Enjoy the experience of being a landlord

Ah yes, enjoyment, easily forgotten for those who have spent the past year watching property values fall and then rents plummet when too much unsold stock came on the rental market. "If people find themselves in trouble, it's because they didn't use their common sense. Otherwise, it's like real life Monopoly. What could be better than watching the money roll in?" Fergus says. You get the feeling he'll know just what that windfall feels like soon enough.