Janice,
You answer will lay in whether or not you will have the ability to carry the lot (plus the construction costs) as well as your current home....without a tenant supporting the mortgage. If your market is like most, the amount of rental homes on the market has gone up right along with sale properties. With the increase in inventory, you can expect a much higher vacancy rate for your home - raising your odds of (at some time) having to cary all of the debt with no support. If you've already purchased the lot, and are comfortable affording it along with your current home - I think the prudent thing to do would be to wait until you sell your current home before you build. That is...unless you're able to comfortably afford all 3.
Best of luck! - Thu Oct 23 2008, 11:53