I used to work for a company that dealt in circular stores, both steel and concrete. WRT second steel stores, sheets must be damage free else they will rust. Need to consider the cost of dismantling, transport and reerection. Plus bolts and sealant. Also need to know the design features of the tank. Can it be extended? If so from the base or from the top? And to what capacity. What sort of coating does it have? Epoxy, glass etc. And if you need it extending can you find a company who will manufacture the extra ring for you and again at what cost.
We dealt with an Irish firm for the concrete stores. Some customers found it easier to get planning for a steel store because of the colour being less of an eye sore. Other customers found it easy to get planning for either, just seemed to depend where they were. The only disadvantage would be that some of the concrete stores cannot be extended and also you need to consider transport cost from Ireland and the labour to erect the store.
Personally I hate holes in the ground. Have seen too many cows fall in on farms where proper gates and fences were left as an after thought.