Average cost of gas for apartments

There needs to be a website that shows the average gas bill for apartments across the country. The above map from the Energy Information Administration comes kinda close, but only lists the price of gas. Not how much an apartment uses.

I'd like a map to break out the gas costs into studio, one bedroom, two bedroom, and three bedroom. Or maybe it could break it out by square feet. This information should be available on the web. I just want to know the average gas bill for a studio in Chicago.