Can I build deck on top of patio?
If the footprint of the new deck fits over the patio, you should be fine with a freestanding floating deck. Precast post blocks like this can transition from the slab to the deck framing, and provide the all important gaps so the framing can dry out:


Consult locally for wind tie down requirements: you'll probably need to sink some anchors into the slab, and add cable restraints to the deck framing : any sort of roof will act as a sail.  Going freestanding greatly reduces headache and risk of attaching to the house.