Although I doubt if the weight of one or two people walking on a structural concrete slab is going to transmit through to the concrete pier causing vibration
You'd be surprised ... don't forget a scope can be sensitive to disturbances of less than half an arc second.
a structural concrete slab would be a much better support for a shed and roll-off roof.
There are other issues here. Frost heave is more of an issue with a large area of slab. Best foundations for a shed are trench founds running under the walls. A wooden floor supported by the walls is good but a free standing wooden floor is better. IMO when the floor is kept reasonably dry covering it with an old carpet is a good way of creating a dust & vermin proof seal with the pillar - the carpet will also help protect your eyepieces from damage when dropped.
