Thanks for your advice, I have decided to give it a miss, I don't want to risk injury to them.
I did buy a plastic platform from my local pet shop but when I got it home I discovered that the ladder was far too narrow at the top for an adult piggy and though Tommy could get up it Sparky would of simply dropped off, though it was only a few inches it still would of been a scary experience for him.
They did have a house with a flat roof but, I don't use it as Sparky is a much calmer and more confident piggy without it though part of his cage roof is covered so he has somewhere shaded to sit.
My main reason for looking for a shelved area was that Tommy tends to wit for Sparky to start eating and then, ignoring the second dish containing the same goodies dives into Sparkies, my thought was if they have seperate areas to eat then would it avoid a confrontation however, watching them this morning Sparky doesn't seem in anyway bothered by it.