First of all, thank you for your donation.
The big advantage of buying off plan is the price is fixed and in a normal market, the prices rise whilst the home is being built without you having to pay anything. It is also highly probable that when the show homes are finished prices will go up and will be increased even further as the site is sold. A March completion is in the middle of half-year and year-end figures so it shouldn't be a rush job either.
Most housebuilders will want to get some sales on the board early on as it breeds confidence for those who visit later that the development is popular. It has even been known that false sold stickers are put on homes and the sales office site plan! So you should be able to get a good discount. Be wary of buying near any social, or as they call it, "affordable" homes. These will probably not be for sale but should be indicated on the site layout.
On the downside you can't see what you are buying rooms sizes etc. If you can go and visit your house type on another site just to be sure it is really what you want.
As you know, Barratt and David Wilson Homes are the same company. Check whether the site manager that will be building your home won an
NHBC Quality Award last year. (Check out the link.)
As far as a deal is concerned, you are always going to be better off with cash. Stamp Duty paid is quite common but works out at 1% (£2,500) on a £250,000 home.
Stamp Duty Calculator It should be possible to get around 3-4% off the listed price.
You might have to have this made up of a discount, stamp duty and perhaps some "free" extras.
Be aware that upgrades and
house builder optional extras are always poor value. In particular, House builder's carpets are always rubbish quality and will probably be "thrown in" not laid!
You could also indicate that a good deal now, will mean you would give a "YES" to Q1 in the 8 week Customer Satisfaction survey!
You are in a strong position, you don't have a house to sell and are very unlikely to pull out.
You are also "green" so in builder's eyes, you won't be expecting too much.
I would ask sales if you are buying timber frame. Normally these are best avoided anyway but one built in the winter months may get soaked and suffer more shrinkage than usual. Squeaking floors are a particular problem.
What you get using 20% Help to Buy has been more than taken up with housebuilder increasing their prices since it stated. You are also paying a premium price for a new home. You can use Help to Buy to get a 95% mortgage at reasonable rates for an older home.
I am delighted for you that you avoided Persimmon. They should refund your reservation fee but may try and justify keeping £100-£250 for admin.