Saving capital gains tax

yes you can claim the exemption u/s 54F of the I-T on the CG arising on the sale of land.  However in this case you are requierd to invest teh net sales consideration and not the Capital Gains i.e Sale consideration Less COA.

As you are constructing the property the time limit would be 3 years from the daet of transfer.  if you are not able to invest the entire sale consdieration in construction of the property on or before the due date of the filing the return then you need to deposti the same in the Capital Gains Deposit Scheme and then utilize the amount from this scheme as & when required for the construction of property within 3 years from the date of sale.