I very much agree with Goodlife's advice. Dip the end of the perches in diatomaceous earth, so that plenty clings on.
It's a bit late now that he's got his coop assembled and occupied, but if he gets a chance, I suggests that he treats the inside of the coop with creosote. It may be worth buying a cheap or secondhand coop to house the hens while he does this, because you should leave at least two and preferably three weeks after application before allowing the hens back in. But if you can arrange things to creosote every year, you'll not be much bothered with red mite. Creosote is horrid stuff, of course, so all the proper precautions should be taken when applying it.
One thing that we do is to have a spare set of roosting bars made up, and give them a good soaking in creosote. Then, when they're thoroughly dry, we swap them in to the coop and treat the other set of bars ready for action if red mite do appear.