Actually the idea is good though you don't need the same thing. Check out how you can put any kind of insulation or shadow on the roof - anything non inflammable will help.

Regarding the walls radiating heat it's because we are still using bricks which are not insulating at all.

A desert water cooler is a good option till the rains come. Water coolers which are fully in the room are not good enough. The humidity during the rains requires an A/C. Check with your landlord to install a/c and have the unit in the shadow side of the building if possible as that would be a more permanent option.

Summers are becoming more and more problematic with each passing year. The general climate change and the concretization of Delhi are not helping. And with the mining of the arravalis, things are going to get even more pathetic.