then install your hardwood flooring. You can level the floor with a new subflooring. Is the floor just running up or down hill or is it wavy in sections?

Using the roofing shingles, I assume you speaking of cedar shake shingles, not asphalt. If you do not have the floor level and de waved, your hardwood floor will be creaking and moving around all the time.

It may even come un grooved in spots. Before putting down hard earned money on hardwood flooring, I would do the necessary and required prep work first or don’t do it at all.