My plan would be to lay a concrete pad to give a good strong flooring and then lay a row of blocks for the shed to sit on, the height of the doorway is about level with my eyebrows. From what I've seen the sliding doors are made of old takeaway trays, so having to make a new door to fill the larger doorway would kill 2 birds with 1 stone anyway.
The main reason I want a metal shed is so I've got somewhere under cover to use a welder, don't really fancy welding away in a wooden shed. Decent metal sheds seem to go for good money, but the Yardmaster is less than £300 delivered. It's either make do with the rather concerningly cheap Yardmaster, or spend the extra and build a shed out of blocks.