Garage roof for squash?

Can you grow squash on a garage flat roof? I was thinking of planting it in some car tyres but wanted to check if anyone has tried this first. My friend recommended using tyres filled with manure but I'm not sure if it would work or not on a roof. The roof receives sun practically all day long but I don't know if they would get too hot trailing along the ground?

I would love to hear if anyone has any views on this.

Thanks.

I doubt they will object to the heat. But as azubah says how strong is the roof. If you end up needing a new flat roof you would do better to buy some squash from a supermarket.

Cheers HH

I will check about the strength!!!

I was more wondering about if it would be OK with regards to drainage to put tyres straight onto a flat roof rather than onto soil? 

Are you short of growing space ? Are you wanting to do some vertical gardenning ?
To be honest, if I were to grow something on a garage roof, squash/pumpkins would be just about the last thing I would put up there. Doesn't make sense.
They need deep fertile soil and oodles of water.