I have five 3 month chicks and i wanted to add them to my flock but i think on elf the roos might have marks
what do i do?
First, make sure that it is, in fact Marek's. Get him tested, either at a vet's or state univeristy.
It is never safe to introduce unvaccinated birds, regardless of age, into a flock that has had confirmed Mareks. Birds that survive infection become life-long carriers, and will make any new birds sick.
If you have confirmed Mareks in your flock, all new birds added must be vaccinated prior to introduction. The vaccine is available for purchase online, and it doesn't cost much at all.