FIRST POINT TO UNDERSTAND IS THAT A PoA IS A DOCUMENT WHICH CREATES ONLY RELATIONSHIP OF PRINCIPAL AND AGENT,in your case your builder being pricipal and you are becoming agent.So legally a principal , under law,has always right to REVOKE PoA executed in your favour.
The next thing to understand is this that a PoA can not confer title to vest in you from your builder as law shuns it,and That can be done only by a registered instrument of sale.
HENCE BY PoA ONLY RIGHT TO USE WILL PASS TO YOU THAT TOO SOLONG PoA IS NOT REVOKED BUT IN CASE YOU WANT TO SALE IN FUTURE,THE RIGHT GIVEN TO YOU COULD NOT BE TRANSFERRED EVEN BY A PoA OF YOURS.
AND IN CASE YOU GO FOR AN IRREVOCABLE PoA THE STAMP DUTY WOULD BE PAYABLE AS MUCH AS ON A SALE DEED.
SO ALL DEPENDS ON THE FACT HOW MUCH YOUR BUILDER IS DEPENDABLE/?? IF DOES NOT HINDER IN YOUR RIGHTS IN FUTURE YOU WILL SAIL SMOOTH BUT IN CASE OF ANY DISPUTE ARISING IN FUTURE, THE REVOCATION WILL TAKE AWAY EVERY THING FROM YOU..