I would put a ring of mulch around the base of the tree. If you do that you will not need to add soil. Sometimes adding soil on top of roots not healthy for the tree.
I am not a big fan of blocks and edging around tree, it does not look natural and is more difficult to trim with the mower.

Here is a link that might be useful: Garden Design Ideas

The picture you've posted does not explain what you're trying to say with words. Everything below the tree is in almost black shadow. It looks like something major is already finished, so not sure what you are trying to do or asking about.

On another note, are you trying to use the tree to hide the house?

The tree does excel at house-hiding.

What house? :) What little bit of house not hidden by the tree is going to be hidden soon by the evergreen at its right corner.

Looks like the tree is WAAAYYY overdue for some pruning up from the bottom. Can you walk under the tree? It doesn't look like it.

I agree with plantman-putting soil on top of surface roots can sometimes be harmful to the tree. A shallow-rooted tree is meant to grow shallow; sometimes trees that have their roots covered will just push their roots up to the surface again.

I think mulch would be your best bet. Do not put more than three inches of mulch on the area and do not pile the mulch against the trunk.

I would not bottom prune your tree. It has a beautiful shape and is growing as it should.

Linda

"I would not bottom prune your tree. It ... is growing as it should."

Based on what criteria? ... how it would grow if it had its own 1-acre field and nothing around to bother it? Here, it's part of a suburban landscape and has work to do in contribution to enhancing the overall picture, view of the house, allowing passage below for cars and people, and permitting space for general maintenance. While a tree that grows wild might be alright where there are no other needs of it, it does not make the best tree where civilization occurs ... even though it would look nice if one looked at nothing else.