Hi you had said, "I have seen other neighbors build up the soil in this area and grew grass, etc - but I have heard this can harm the Oak"
You can build up the soil level safely around the
tree as long as you do not change the surface level where the trunk of the
tree meets the ground. The trunk portion of the
tree has a different bark then what lies under the soil. The bark below the surface is actually water proof, and the bark above is not. The bark above if kept constantly damp will eventually rot and "girdle" your
tree, killing it. Many people do the same thing by putting mulch down too deep at the base of a
tree as well.