I have a cement slab that is rough and uneven. How can I put brick over it to make a patio?

I can foresee a couple problems with doing this. The uneven condition you have now may telescope up into the pavers, a thick sand bed may even it out if it can be compacted flat. Drainage under the pavers may also be an issue as freeze / thaw cycles may move the pavers if the moisture cannot escape. The right thing to do would be to remove the slab.