It depends on a lot of conditions. First, I should know what kind of metal is there. There are plenty of decisions you can make but they are different only because of the type of metal. I also had such problem, but my drain pipe was stainless and that was really complicated to do it. But first I had a consultation, my uncle knows what to do. I can't ask him now, so try to search information. BTW, I bought one of my carports, two years ago, I like it the most, I bought it at
carport Sydney [carportaustralia.com.au], so try to ask them.