Riven slabs - what is level? - Can anyone help clarify what's ok?

[Kev the fitter]

Hi All
I'm laying a patio for which the customer has supplied reclaimed concrete riven slabs. The rivens on these mean that on a single slab one corner can be 10mm thicker than the other three.
Logic tells me to try to avoid any big differences on adjacent slabs but that there will inevitably be joints that are uneven. Please note that the slabs do not all have the same rivening. (if that's a word).
Would I be right to lay these to an overall level as described in the main site, with a slight fall of course, or is there a way to avoid any potential 'trip' hazard joints? The page on riven slabs says they should all have nice level joints but I don't think they are talking about slabs like these.
Customers, who'd have them,

Thanks

[lutonlagerlout]

kev as with bricks you lay to the leading edge
so in this case its the top that counts
i find it easier to lay riven slabs to a line and the same as with a hand made brick you just use your judgement
a long level can mislead as it only takes 1 misshapen slab to throw you
so set a course up along the house say
150mm below dpc
then set a piece of timber up in the garden or 2 lamp irons
and make sure you have around 1:60 fall i.e. over 4 metres you need around 60-70mm of fall
then work your way across
hope this helps
LLL

[Kev the fitter]

Thanks LLL

I guess it's a case of making sure the customer knows my concerns and trying to ensure they know what to expect, just that the top surface is so uneven I don't think it's going to be much fun

Kev