i need to move my caster oil plant. is it ok to do so and how deep do the roots go? it's young with only 4 branches

Can you move the shed?. If not wait until the autumn.

I always thought ricinus was an annual, at least ours always die in the autumn and we grow fresh each year, or they self seed. You really should try Zanzi Palm which is an enormous plant growing to ten or twelve feet (or more). Anyway, rather than move your Ricinus I'd grow another one or two from seed as they are so easy and grow so rapidly.