Some of the great thinkers have argued that there are seven great stages in the life cycle of humans, stretching from cradle to aged infirmity.

But as far as the building industry is concerned, there are only four key stages in the life cycle of the new home buyer.

The first-time buyer is key. When someone puts their foot on the first rung of the property ladder, they are poised on a process which will take them a few steps up the ladder in terms of house size. But towards the end of their lives, once the family have gone, many people take a couple of steps back down the ladder into something smaller.

After a period when sales to first-time buyers in Scotland faltered, this group is now cautiously emerging back into the market, according to the TSB Bank's Scottish House Price Monitor.

Sales slumped last year, probably due to uncertainty in the run-up to the General Election - combined with increases in interest rates and worries about potential abolition of MIRAS.

However, things started to pick up again over the last six months.

House builder Barratt says that first-time buyers in Scotland have become much more choosy.

Barratt Northern chairman Mike Norton said: ''Although first-time buyers may be on a smaller budget, they know exactly what they want. They like attractive, traditionally-styled homes with a modern interior and features such as a good sized lounge and double bedrooms.''

Location is another important issue for the first time buyer, since they want to be able to sell the home as easily as possible when they need to move up the ladder.

The arrival of children, or a new job and a bigger wage packet, are two of the factors that often drive a move up the ladder.

Several major builders have been re-designing their homes over the last couple of years, many of them in a bid to ensure that they meet the family needs of today. Stewart Milne Homes is among the latest to overhaul its house styles, using market research to shape the company's new priorities.

Sales and marketing director Marlyn Boal said: ''Through focus groups and our own observations we confirmed that potential buyers are price conscious but equally importantly, they expect far more in their home than before.''

Custom-designed bathroom furniture, built-in wardrobes in most bedrooms, gas central heating with individual thermostats, fully fitted kitchens, monobloc driveways and additional TV, power, and telephone points were all high on the agenda.

For many people, achieving that house with two or three bedrooms is enough. They are happy to put their feet up and stay there for the rest of their lives. However, when their earning power is at its highest and their children are still at home, many professional or executive people decide to make one more big move upmarket.

This is the sort of move that shows you have really made it. Usually with four or more bedrooms, maybe three public rooms, two or three bathrooms, double garage, and an interesting interior layout are all signs that you have made it at last.

Some builders, such as CALA, Bett, Bryant, or MacTaggart & Mickel, specialise at this end of the market. But many other builders, such as Tay Homes and Stewart Milne, can offer homes right across the price range.

Most of us would consider ourselves set for life when we had reached the stage of paying more than #180,000 for our home - which is where the top end really starts.

But come retirement and everybody has a decision to make. The kids will have flown the nest. Do you really need that big house? Is it worth paying top whack on council charge and running costs when you have to rely on a more limited income? This issue is becoming even more important as many people opt for early retirement and have to make a limited pot of cash go further.

Trading down into a smaller home, or a flat, is a prominent trend as people decide to ''cash in'' their larger house to create some capital for investment.

Many such buyers simply trawl the market for what they require, but others go straight to specialist retirement developers such as McCarthy & Stone.

Currently celebrating 20 years in the business, the firm now has a 70% share of the purpose-built retirement market. A combination of convenience and security are the key selling points.

And those are the two key selling points which buyers at every stage of the property cycle are seeking.