Schiller,
Anything is possible it depend on how much you wish or want or can spend on such a structure,
Options:-
Full time Structural hangar, if peak(Apex) of roof kept below 5 mtrs then no PP required over 5mtr then Full PP needed, this would cost you approx £25 to £45 per sq foot (footprint) depending on what you wanted
If you have an existing building you could go for a PVC/Canvas expanding (incl Roof) add on loading bay, no restrictions via PP for this is a temporary structure, these are large enough to house full time full size Artic and trailers so would cover most Helis, cost here would again depend on footprint but would range from say £12k upwards size and height being the controller all you need is a dead flat concrete surface.
I have built full time portal frame hangers and provided soft skinned ones, it really does depend on what you want, and are prepared to spend.
Peter R-B
Vfrpilotpb