We bought a small unit which has a red steel roof. Now we would like to replace it to tiles instead.
The quote (from a Gerard certified roofer company) says they will leave the steel roof there and they will put the tiles on the top, because it's cheaper in this way.

My questions: is it okay to do like this?  Of course they will give guarantee, but is this the normal method or usually people are removing the old steel roof and then install the tiles? I mean will the roof become too heavy or not?

It's a professional company so I trust them, but I am from Europe, where you hardly can find any steel roofs, so I dont know anything about how to replace them.

Please have your say, much appreciated.