Off-plan sales are a sign of a strong market and a delight for developers. Buyers commit to pay bricks-and-mortar prices for what is still a piece of paper. They are tough to achieve, however. Purchasers have to be sold an idea and the developer has to be able to offer a house's-worth of trust. Developers that have been around for years have a head start.

Cala has been in existence for more than a century. It started as the City of Aberdeen Land Association in 1875 and was the first Scottish company listed on the London Stock Market. It is seeing good off-plan sales of its one- and two-bedroom apartments and three- and four-bedroom houses on the Millbrook Park development in Mill Hill. Buyers so far have included investors and commuters.

Apartments range from 538 to 1,733 sq ft, with prices between £414,950 and £899,950. A four-bedroom terraced townhouse is available at £1.095 million. Agent is Preston Bennett.

Buyers also trust a developer with a strong brand. Heronslea, which has been around for 20 years, has made the bulk of its sales at its two sites in Bushey Heath off-plan. It specialises in providing downsizers with apartments. Its schemes at The White House and Windmill Place are now followed by Renaissance, eight three-bedroom apartments in landscaped grounds in Hadley Wood.

Retired Hertfordshire couple David and Sheila Speker recently purchased a two-bedroom apartment off-plan at the White House. They had previously lived in Radlett for 12 years.

"Our family home had become too big for us," says Mr Speker." We wanted a bungalow but couldn't find anything we liked, so we started looking at apartments; we wanted something new with no maintenance. When we came across this development we were really impressed and knew straight away we wanted to live there."

The White House, in Sparrow's Herne, has 16 one- and two-bedroom apartments in a modern four-storey building. Each has a balcony or terrace, with views over surrounding countryside. There is gated basement parking and a video entry/alarm system for each home. Inside the apartments, layouts are varied; some have open-plan kitchen/lounge areas, others have the lounge separate from the kitchen/diner.

The Spekers chose a two-bedroom ground floor apartment with a patio at the back.

"We liked the location and the area as well as the amenities of the development," says Mr Speker, especially citing the basement parking with direct lift access and the storage space both in the basement and apartment.

"Our only concern was buying off-plan, something we have never done before, but Heronslea has been really helpful and guided us through the process. We had seen other developments but were impressed with the quality and finish at the White House."

The development is close to Bushey High Street and a 15-minute drive from Watford town centre. Prices start from £415,000 for a one-bedroom apartment and from £550,000 for a two-bedroom apartment. Agent is new homes specialist Preston Bennett.