Voluntary registration of gst

I have a land in Maharastra but I stay in Karnataka. This land I have given to a builder on JV at 40:60 ratio wherein 40% flats will be given to landlord. The builder will construct all the flats and give me 40% of the flats in lieu of the land. Do I need to voluntarily register for GST ? so that on the construction cost the builder and the landlord will get ITC which can be set off when we sell our respective portions. If yes, should the landlord register in Karnataka or Maharastra ?