visa's have nothing to do with wanting to build on leased land...
For example, I can be in the Netherlands (not having any kind of Indonesian visa) and via the internet/notaris/real-estate agency lease land here in Indonesia.
maybe you can research the following :
Hak Pakai - Right to use.
Hak Guna Bangunan - The right to build and posses a structure on land owned by others.
Hak Sewa - The right to lease/rent a building.
Short answer = for you to legally build on leased land, would require that you start a PMA company...Now in regards to visa's, with this PMA company you are also entitled to a KITAS...with this KITAS you can legally stay 12 months in Indonesia, in the 10th month you go the kantor immigrasi and apply to renew/extend your KITAS. Downside, you have a company in Indonsiammmmmm`