When you first buy a home, you may just look to get your foot on the ladder and possibly are not thinking too far in to the future. It may be that you have bought a one or two bedroom house but now with to start a family or already have one child and are hoping to have another. IF this is the case then you may find that your house is no longer suitable for you and you need to either move to a larger house or extend your current one.
You need to first work out if you would be able to extend and then how much it is going to cost. It may be that you already have a single story garage that has foundations that can cope with another story. If this is the case then the cost may not be as much as you think. You would also need to apply for planning permission which, you should ensure you have before starting any work.
You may instead decide that you do not want to have an extension and would rather buy a home that already has enough rooms for your and your growing family. This is often the easiest option but does incur the cost of moving and you may find that you don’t get as much for your money as you first thought.