Save the Trees That Are Save-able
Tree wells were used many years ago to attempt to save trees within fill areas of construction projects. They were pretty – usually stone or rock circular structures. Most only extended a few feet from the central trunk, so the roots within the drip line were covered with new soil. None of them saved any trees, so they discontinued using them. I can’t recall seeing a single tree wells constructed at the drip line of a tree—ever. It would be too expensive to create a wall that diameter. Window wells work. Tree wells don’t work.
If the grade will change more than 3 to 6 inches around a tree root zone, then the tree will not survive. Go ahead and remove the tree and replant something nice to replace it.