Choosing females that get along.

how do I go a out choosing females that will get along when breeding and probably raising there young? If I stick to hooded rats, will I keep away from megacolon and other deseases?

Well nothing is absolute when it comes to breeding and genetics but personally I've never had a problem with any hooded rats I've had in the colony.

As far as having females that get along there's just no real way to tell ahead of time if they will or they won't. Buy two that are littermates and about the same size, that should help. Even with that rats will scuffle a bit to sort out whose boss rat of the enclosure. As long as it's only a bit of wrestling and so forth and not real biting, then it's fine and very normal stuff for such social animals.