Hi John,
to NGA
It seems to me that if you lay the sod at the same height as the pavement, you will end up with water lying in that junction and even backing onto the patio. What's working against you is the height of the grass itself. And as the turf builds up, the problem will be worse.
A French drain seems like a reasonable solution to me. It would be better yet if the home owner would let you install a gravel top or French drain cover over the drain. It would only need to be a couple inches wide. I think if you put grass back over the drain, it will work only until the grass gets thick.
