Should be ok then, as all Agricultural PD now requires Prior Approval it would be prudent to include a covering letter giving basic justification, for example, my shed holds 1000 small bales and last year I needed space for 1200 and this year I expect the same problem. Doesn't need to be any more complicated than that but most councils are requiring it now rather than letting new structures to go up carté blanché.The last PD I did was in 2014 for the 100x50, nothings been built or applied for since so I should be ok then I think !.