Exterior flooring ideas

Hi all,
Here's the situation:-
I have a terrace butting up against my house which is formed by railway sleepers perpendicular to the house.They are cut into the house walls and are supported at the outer end by brick pillars and end up hanging over my garden by about 18 inches. The garden is several feet below (The scene of an interesting accident when I was building this-still it only resulted in several months off work and a knee damaged for life! The joys of DIY!)(When you're a clumsy sod).
There are wooden joists running between the sleepers and the surface is formed by 6ftx2ft panels which are a 'sandwich' of dimpled steel about an asbestos filling - taken from a demolished garage - I didn't want them but my father in law had already struggled to deliver them to me as a 'surprise' so I felt obliged to use them. They weighed a bloody ton !
This terrace has no noticeable flex and has stood there for about 4 years.
I originally covered it with grooved decking. However, all the planks 'cup' in hot weather, I am assuming because they dry out where exposed to the sun, but can't underneath because of being in direct contact with the metal panels. I realise I should have placed battens underneath them to provide ventilation. This would have meant though that the deck would have been very near, if not at, the level of the DPC.
So I ripped it all up this week and need to start again. The panels are not exactly aesthetically pleasing and need to be replaced with something.
Any ideas ?
I have considered flags. But even thin ones are going to be heavy - and how would I fix them ?
I it possible to pour anything over and decorate in some fashion ?
Exterior lino ?
The requirements are that it should be relatively maintenance free, non-slip and be able to resist stray glowing charcoals from the barbecue !
TIA
Steve.
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Sorry ! I mean that the panels need to be 'covered' with something, not 'replacing' - far too much hassle. Steve.

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