Hi Britbadboy,
I'd add that as with most things you need to go into this with your eyes open and with a realistic view of what the house purchase process will bring.
From what I have read of GW. It does employ some sharp selling practices and whilst everything is nice now that you are interested, you need to take care before committing yourself too much.
You need to be sure that the 'good price' you are getting it for is the realistic value, (as is the pre discount price). New builds are said to attract a slight premium when new, but this is lost almost immediately.
It is worth haggling / negotiating hard with the builder as to the price and what you are getting for that price (carpets, furniture, stamp duty paid, mortgage paid for a year etc) as with other offers.
When you buy, you will be expected to put down a deposit (about 1000 or so), and on exchange (anywhere from 2-6 weeks) you will need to provide the 10% deposit.
You should arrange an independant solicitor to act on your behalf (although this may be a part of the offer) to ensure that there is no conflict of interest with the builders interests.
There is generally no guarantee of when the property will be built if you are buying from a plan and looking at a show home, however if it is already done that's one battle avoided. Also if it's already done make sure you have a good survey done, and inspect the property fully yourself (noting any issues) to get these addressed / or discounted from the price. Whilst the NHBC will cover major items, you will also need to do a snagging list when you get the property, before you complete if it is not yet built.
Also with areas of new development, green spaces, parking and roads are sometimes the last things to be completed, so be prepared for that, and also continual buliding if other phases of development is not yet complete.
You are certainly doing the right thing searching the internet and these forums for advice.
You can always ask GW for a timetable of when you can expect to exchange contracts (when you are legally bound to purchase) and when you will exchange (when the property is actually yours).
Good luck with it.
Sparky