[dm_jadhav]

I have heard that, list of "Private Forest Land' Survey nos. is available at the Registration office at Talaopali, Thane. First get the Survey nos. of your area from builder and go and check there in that list. Moreover anybody who wants to book flat in such area will not be able to do registration because it is totally stopped.
Some flat owners are selling such flats assuring that registration can be done in future. But this way is risky and suggest not to buy such flats through resale.
Regarding your second query, you would never able to from builder that land comes under forest. Even builders did not know this when they bought it. Ultimate solution is check with reg. office.
Good that you people know that there is something like "Private forest land". When we boubght one such flat we did not know.