Compared to the rest of the Washington D.C. market, the Ashburn region has less expensive rates, so you should have no trouble finding a great deal in this depreciated region.
In the last 90 days, 20 listings have been posted online, which means spaces most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. There aren't many listings below 2,000 square feet available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,290 sqft. Most properties in this market are around 2 floors. Most buildings in this area were built in 2001 and are Class A.