it is noted here that service by way of renting of residential dewelling for use as residence
In first scenario when bill is made by you
in this case you are acting as an agent & using the residential complex for fulfilling your commercial purpose not for your own residence , which will attract GST compliance .and you will be charged by the owner the applicable gst rate 18% on total value of residential complex taken on rent ,
On commission /brokerage charged from the ultimate buyer you have to charge 18% . & the rest of ITC available to will vanish.
2. when billing is made directly by owner to ultimate tenant
On commission /brokerage charged from the ultimate buyer you have to charge 18%.claim itc if any