I think he meant you roll gems till you get 5 random legenday heroes
It seems to me that using my gems 450 at a time to hire 3 heroes is the best use of gems and best chance for getting Legendary heroes. Only other thing I use gems for is to get more than 2 builders. Buying heroes with gems 450 gems buys 3 heroes. I got Aries, Beast Tamer, Dracrax. Sometimes all 3 are worthless but then consume them to raise talents.