Welcome Casey Wa:
Do I hear you wanting to place concrete on top of the deck? That just won't work, no way jose. The best way to make a hard surface patio is to remove the deck completely right down to the foundation. Once the deck is gone you can fill the foundation with crushed limestone, sand or pea gravel. Build a concrete form around the foundation that will allow the patio to overlap the foundation by 1-1/2". Some suggestions for the patio; exposed aggreate, flagstone laid on top of it, some choice of nice tile or granite with grout lines. Let us know how it turns out.