I've read and heard of paver / stone patios being laid over an existing concrete slab. If the slab is in good shape, it may be fine but it'll raise the level of what goes down on top of it and may need to "step up" onto the end product.
Do yourself a favor if you are shopping installers for pavers, look for an ICPI Certified Paver Installer for at least one opinion/estimate.
Here's a link that might help if you are not familiar with ICPI.
http://www.icpi.org/homeowners/
I'm not affiliated in any way with any of this.
Although still not guaranteed to have it done correctly, I used it as a starting point for beginning our installer search figuring it's cheaper to have it done right the first time than to undo / redo.
Good luck!
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Crank awning
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