If it was mine I believe I would completely disassemble the wheel and try to make the rim round and laterally flat. How well this can be done will depend on how badly it's bent or warped. You may need some wooden blocks and a rubber mallet. Or you may be able to grab opposite sides of the rim and push it against a big tree. Work slowly and correct the shape of the rim a little at a time. Any improvements you make to the shape of the rim will help with evening the spoke tension and with lateral and radial truing.

Keep the hub to rim spoke lengths as even as possible, especially during the early stages of building the wheel. Remember that it is possible to have even spoke tension on an out-of-round wheel, even if the rim is perfectly round and flat. Keeping the wheel round is most important during the early building process. Even tension, dishing, and lateral truing becomes important during the last phase.