Can't find the title of a dragon book i'm looking for?

i remember bits and pieces and want to recommend it to my friend. I remember that there are some "great" dragons and some lesser ones. there are i think 5 great ones, one is a dragon of drams, one is of time, one is black and is evil, i want to say that the red one is the dragon of life, and i cant remember the other one. i remember that there is another red(i think) dragon who can turn human, and is the oldest elder or mage. he can communicate with people with a talisman that has one of his scales in it. i think that there may also be a human mage who is somehow special and has to go on a quest, which at one point involves two goblins in a hot air balloon that the black dragon kills. the black dragon can also communicate via the scale in the amulet as well. the goblins hold the red dragon of life prisoner, taking her eggs and training her young to be warrior dragons. the mage i believe had a name that started with an R