making gaskets

I was cleaning out my old mans garage the other day when i came across a flatbar of brass about 20cm by 10 cm by 8mm thick. Also a copper plate 40cm by 12cm by 8mm thick. He had them forever and told me to just recycle it. Im thinking about cutting my own SR exhaust gaskets from them. Which would be better brass or copper? I was thinking because of the sizes the copper for the exhaust manifold and the brass for the turbo gaskets. What possible problems might i face? Is this even a good idea?