Unfortunately, you're at their mercy. Obviously you aren't going to back out of the purchase of the house over two more weeks of construction, but it is aggravating as hell. Unless you have a definative completion date established with monetary penalties for not hitting that deadline...your only two options are cancel the deal or wait. Sorry.

__________________
Though I am different from you,
We were born involved in one another.

For it was not into my ear you whispered, but into my heart. It was not my lips you kissed, but my soul.

Complete surrender should not just come at moments in which one faces overwhelming odds, but in the calm when it seems one is personally in complete control of one's life.