I'm building a deck onto a house that is 6 inches off level from end to end. The deck will be in two parts, one ground level and one raised under the patio door. I can't build the deck level or the house will look off level. Is my only option to build the deck off level to match the slope of the house. Obviously leveling the house is prohibitively expensive.
I'd say you can slope the deck a little, but not too much. I don't know how much slope I'd consider acceptable, without first walking on different pitches. If your house is 40' wide and 6" off level over that 40', then that isn't a ridiculous amount to be off. But if your house is only 20' wide, then 6" of slope is a bigger problem.
I'd be more inclined to make the deck level, assuming the house isn't drastically out of level. But without seeing all the detail, can't say for certain.
Is the house continuing to move, or has it stabilized? One way to tell is if you have engineering report from the past to compare with a more current report. Sounds like you are in the area now of having difficulty getting next owner financed should you sell.
Back to the deck - think about splitting the difference, making the deck 3" out of level. This way it does not visually show as badly, and is not so bad to walk on. As said before, it depends on the length of the run for the 6" as to how noticeable.