Question on registration stamp - flat tamilnadu

hi
i bought a flat in tamilnadu and registration was done recently.
i bought it through a builder.
i see the sale deed was registerd in some  20rs stamp paper and the same was also registerd in a stamp paper of
higher value (10k stamp paper)
what is the needed to create in two differnet value of stamp paper for sale deed..
some builder, i heard, do it only on 20rs stamt paper only.
please advise on the differnece and what the registration law says this rule