Most new construction homes in the area are 3-4 bedroom homes. There is alot of inventory (especially new construction) on the market. However, with that said the Chester County Market has held its value in this tough economic turmoil. I do not know enough to comment on what you could find in the Great Valley, but it has the best school district out of all three areas (although all are excellent).
If looking in Downingown school district you will be able to find a 4 bedroom 2.5 bath single with aound 2500 square feet for that price. In fact I would look at Chester Springs, its a very desireable area. This area has a ton of new construction which if you pick up now, in a few years once the inventory sells out, there will be a ton of upside.
Take a look at Byers Station as one option. However if you want over .25 acres look to West bradford or East Brandywine in Downingtown school district. Hope this helps some. I am not sure if I am allowed to post links here, but one website I have used to look at property is
www.thehousecouple.com
it allows you to search by school district and limit to new construciton. Note i am not advertising or reccomending the realtors that sponser this site as I have not used them.
I am not sure if you are from the area, but as an investor I have bought heavily in the area and just want to extend somthing to keep in mind, TAXES.
A new construction home around 425 k this is what to expect to pay in taxes each year.
Downingtown Area: around $7,000
West Chester: around $4000
great valley: not positive but probably in the middle
Also after you buy new construction appeal your taxes to the Chester County Assesment office and they will be lowered by about 15% (ask your realtor about this as they can help you)