My cat climbs onto my roof and sleeps there.. need advice.?

Well basically it has two routes, First route it goes outside through its catflap and jumps onto a bin, garage and finally the low end of the house roof, then it walks its way to the top of the entire roof near the chimney and sleeps there... the second way is if it sees one of the windows opened (Upstairs of course) theres a little ledge it goes onto and jumps onto the roof.. it sleeps at the top and i think its dangerous because what if hes sleeping and slides/falls off..?? what should i do because i dont like locking my cat indoor 24/7 its just not right cats should have freedom.