The statutory order of a 1031 is this: a sale followed by a purchase of investment real estate. You can’t exchange into something you already own, and you can’t exchange into construction on real estate you already own without a different approach.
In a reverse exchange, the qualified intermediary forms a holding entity called the EAT (exchange accommodating title holder). This EAT takes title to the lot you want to build on. The property is under your control, but you’re not on the title yet. Then you construct the building on that property. Now you complete your sale if you haven’t already, and you “purchase” the lot and building owned by the EAT for exactly what was paid/spent on it. By doing this, you are able to maintain the integrity of your exchange and also purchase the exact right replacement property.
Timing, complexity, financing, and cost are all the issues you’ve got to wade through. But reverses can be a pretty powerful tool to get you right where you want to be. Nonetheless, it might be worth talking to your tax expert about structuring a more straightforward 1031 exchange.