Blue Gum is Termite resistant and good for roofing. However, it is prone to warping and bending if not dry. Additionally, thinner pieces will split at the edges so you need to be careful when buying.

i bought a number of blue gums from a farmer in olkarou. Iam yet to cut them down. What do i do to ensure they dont bend on drying. Am not sure of their age.

@am66,
BG has many disadvantages when used to roof.

1.Weightier than cypress hence very heavy roofs.
2.Warps.
3.Twists.
4.Splits.
5.Difficulties when driving nails through.
6.Sags

Since you are not going to roof your house every election year,disregard the price of cypress and go for it.I also believe you want an even and beautiful roof.

I cleared roofing early this week including putting timbers for ceiling. I used Bluegum and the outcome is okay according to me.
When buying, make sure you buy red blue gum timbers and not the white ones. They are better. Termites is not an isssue

Did my roofing some months ago with blue gum.
My fundi had discouraged me as there was more work for him.

True you will need more nails and more fundi time. As @kwanini has said straightness depends on the cross members and all other supports.

Just 2 tips from me.
1. buy long blue gum pieces i.e 15ft and above only. Short ones are a headache to keep joining.

2. For the wood where the tiles will be nailed on, dont use blue gum. The nails will damage the tiles as possibility of nails bending is very high. If this happens leaks will be constant in yr house.