Buying a property off plan (ie before it is built) was at one time the only option when demand exceeded supply. However things have changed in the cyclic world of property.
If you think buying off plan is right for you - fine BUT as the market has now slowed down it is apparent that some builders have slowed down their building projects and in cases stopped building.
This means that your completion date may well be delayed (probably in some cases VERY delayed) If you are not in a rush to complete then you do not have a problem but if you want to move in or start letting it out you will have a problem.
Also ALWAYS ensure when buying off plan that the monies you pay in advance are refundable if the project stops. This is the law and must be arranged via a bonded bank account. Dont be fobbed off with any excuses you want a cast iron guarantee your money is refundable. Take proper legal advice if could well save you money.
Also the idea of buying off plan and selling on prior to completion is very much under legal scrutiny and in some cases may prove to be impossible - again if this is your plan you will need guarantees that this is indeed an option.
If you think buying off plan is too risky for you then you are lucky because there is now plenty of choice of new ready now fully legal property (and so can have a mortgage) They come with a builders 10 year guarantee which again is law and is organised via the local town hall.