I suggest you contact an agent for a market trend report. That report will show how many properties sold in each price range over the last 2 years, and can help you decide whether or not now is a time to sell.
If you are able to hold on to the lots, then I suggest you do. Depending on when you purchased the lots, my guess would be that you will have to sell them for less than you bought them for, because prices have come down since the lots were originally sold, after Hurricane Katrina.
Round Rock is also not an area that spec homes are moving quickly in.