Buying a brand new house is never a "sure date closing" transaction, the right thing would have been that you never release yourself from the place you are renting until after closing. That is always my advice for my clients when they are buying a brand new construction, yest, you lose some money paying for 1 month extra rental, but what would you think is best, lose 1 month of rent and have time to move from one place to the other or be "homeless" who knows for how long until the closing actually happens? Here are your opitions:
1- Move in with a relative.
2- Try, re-rent the place you are now.
3- Look for a place to rent on a month-to-month basis
4-Hope that it will close before you have to move(these dates always change with no notice, so maybe you will be lucky to have a closing before you expect)
Also, try talking to your attorney to see if he can pressure the builder's attorney to expedite the closing date with a "time of the essence" notice, or any legal advice he/she can give you to help you.