I´m no expert, but I am under the impression, that western parts of Sudan, and all of Chad, are dodgy to say the least, and tourists may not be allowed entry at all. Even if you managed that, crossing into Libya from the south could be yet another bureaucratic challenge. Plus there is the largest desert in the world, that your route would cut in half...
I toured parts of Southern Africa some 7-8 years back, and Michelin maps of the continent seemed to offer pretty good value, might help you with the planning. From Cape Town up to Namibia, Zambia, Zimbabwe and about halfway north into Mozambique the roads were actually pretty good, or at least they werent terrible... but I hear that central & northern parts of Africa can be a very different story.