As per Para 5 of SCHEDULE III of the CGST Act 2017 :
"Sale of Land, and subject to clause (b) of paragraph 5 of SCHEDULE II, Sale of Building."
Hence, Sale of Land or Purchase of Land is not treated as a SUPPLY under CGST Act 2017 and no GST leviable thereon.
Moreover, Land neither satisfies the definition of Goods nor the definition of Services as laid u/s 2(52) and 2(102) of the CGST Act 2017 respectively. So land is neither a Goods nor a Services; and GST is a Tax leviable on the Supply of Goods or Supply of Services or Both.