Flat(ish) roof - is taht gonna be a poblem (water runoff)?

My roof is quite flat:
I'm a bit concerned with water runoff .... should I be ?
Would it be a good idea to add a little bit of slope (shims) before adding the exterior skins ?
I'm thinking flat is not a great idea, ion the other hand lots of RV's appear mostly flat.
Thanks.

I'm a bit concerned with water runoff .... should I be ?
Would it be a good idea to add a little bit of slope (shims) before adding the exterior skins ?
I'm thinking flat is not a great idea, ion the other hand lots of RV's appear mostly flat.
Thanks.