Ok, this may hurt a bit,
I always ask folks, if you do not have the funds to do it right the first time, do you have the funds and the time to fix it the second time?
water issues around the home are the biggest problems you can face. I'm sure this is nothing new to you, but I just hate to see folks waste time and $$ on a dream I know from experience will have problems after you build it.
If you have frost, installing a deck on a slab is a bad idea, it will only continue to move and fall apart.
To do this right,
Remove the slab and fix the grade below a deck with piers and a wood structure underneath.
Or, Mudjack the existing concrete and install brick or patio pavers over the top of the slab. Sometimes this is an easier solution.No deck to stain or protect, easily removable to gain access to the pit, and water drains away.
And patios are not a TAXABLE property structure, and need no permits like decks do.
Hope this helps,