Ho-oh is A Legendary Pokemon, and MOST Legendaries cannot breed at all. Sadly enough, Ho-oh is one of these! The most popular able-to-breed Legendary would be Manaphy! Breed Manaphy with a Ditto and the Egg will contain Phione! (Phione Does not evlove into Manaphy). Manaphy is only available during special distribution events.
For information on Distribution events, go to:
I hope you like that i put a link! (Site is totally friendly and available for all age use!)