It sounds like you're considering making a purchase in the Brambleton area. Brambleton is a great area, and ultimately will appreciate because of it newness, it's proximity to the Dulles corridor, and the infrastructure that they've been building out in the area.
While prices have started appreciating in some areas closer in to DC, I don't think you're going to see any consistent appreciation in the Brambleton area within the next year. Pries will probably remain fairly flat out there in that timeframe.
Good luck with your plans,