No. When the grass decays, it leaves holes in the dirt, which in turn may be come sub-surface erosion channels. Then one day the whole shebang collapses a few feet, with you and the lawnmower in the resulting sinkhole. Or the erosion channels undermine the retaining walls and the walls collapse. Pile the weedy sod somewhere, root side up, and cover it with a pile of something compostable. In a couple of years, use it somewhere.

Usually, when you excavate the area you establish temporary stakes with needed pitch n height at the house where you need to be. As you start installing the base. etc you put stakes around and mark the stakes with the needed pitch as it declines. After the base is done, you tie a string from the building and run your pavers following the string height. Good practice to have a transit and take elevation shots along the perimeter as you go to make sure the string maintains the needed pitch. Good luck

Thanks Dave! How did you design that?

Michelle Roth , I'm going to retract my comment that the materials may not look good together. I'm posting pictures of a house that was for sale nearby that used pavers and river rock. (so not exactly flagstone but a similar). When I saw this listed on the MLS, I was wowed and thought this looked great. I wasn't thinking "Oh the materials are different." lol. (fwiw, there are pics that show off the yard better. I'm uploading the ones with the biggest swath of materials, so you can see). I think your contractors are probably right, that's the uneven flagstones could cause problems set in sand. If you're going dry-set, pavers can fit much closer together, so fewer weeds! Plus dry-set is permeable, so better for the environment. (rain can return to the water table). I think it's also easier to lay vs. concrete. I'm going to be re-doing my backyard patio later this year. My landscape architect said that cost-wise, the cheapest is stamped cement, then pavers, then stone. In addition to the cost of the stone, I think the labor is a lot more, trying to get everything to line up. Thanks for starting this thread. It's helping me decide. I think I'll do pavers set in sand! ;)