Grape Virgin

I've just ordered a grape for my new greenhouse. Never done them before. Any tips? I used to think the roots had to be outside - is this true? Why?

Hi,
I planted my vine 2 months ago with the roots outside the greenhouse and as Gobs said it keeps the roots cool and allows the rain to water the plant.
This is the way I am going to train mine hope it helps.

On planting (winter) cut the leader to a strong bud on ripe, firm wood. Cut any side shoots to two buds. Throughout summer tie in the leader, cut laterals to five leaves and side shoots to two leaves. Remove any flower cluster. Repeat this the following year.

In the third year (the vines can begin cropping.)
In winter cut back all laterals to two buds, cutting the leader into ripened wood. Summer prune non-fruiting laterals to five leaves, and fruiting laterals to two leaves beyond the fruit cluster.

I hope the greenhouse is very big. Vines should be ok outside on a south facing wall, the more sheltered the better further north. They don't really need to be under glass. That way you get more room for your toms etc.