Information about your climate, site and type of patio are necessary to accurately answer your question(s).

How old is your home? It can take 3-5 years for construction backfill to completely settle. Building a patio earlier may lead to issues.

Concrete or Pavers? So long as topsoil was removed and the base compacted correctly there will be no drainage provided water from the patio can run off into the lawn.

Planting beds agsinst your home won’t be an issue unless there are agressive shrubbery with roots undermining the patio.

Thanks for your reply. 

The house is 30 years old. It is a paver patio set in sand. We are planning for surface runoff drainage as the patio slopes away from the house. Rainfall is fairly heavy in my area. 

I was concerned that rainwater from the upslope garden beds against the house and seeping between pavers might stagnate under the patio, because the base clay-rich soil has a zero grade. And that over the long term this water might erode the gravel base and potentially destabilize the pavers.

Yes, clayey subgrade soil should definitely be sloped, and your reasoning is spot on. But most soil type subgrades should be sloped anyway from a practicality standpoint. A paver patio should be sloped 1/4"/ft, so if you were to have a 16' deep patio, that means nearly 4" of fall. If the subgrade is level, that means the gravel base will be 4" on the shallow end, but 8" deep on the high end. That would require a method of compaction in lifts and an inefficient method of digging out for the gravel base in the first place.

No settling issues, that’s a big plus. The grades 3onthetree suggests are right on.

Polymeric sand is recommended filler for pavers. Very little water will infiltrate nor will weeds grow.

When building our patio a retaining wall was necessary and it was backfilled with compacted stone. Additionally a French Drain was added to carry water away and empty into a lower point.

I’d pay close attention to the drainage detail here. The finished patio should direct water away from the house, and the transition near the foundation needs to be handled carefully so water doesn’t collect against it. The planting beds between the foundation and patio are also worth discussing with the contractor since they can affect drainage. I’d have the contractor explain the slope in terms of the finished patio surface, not just the subsoil and gravel, and make sure there’s a clear plan for where the water will go. If you’re in the Twin Cities area, you could also get another opinion from Minneapolis Decks before the work is finalized.