WELL... If I was going to make a Dragonball d20, not necessarily DnD compatible, I would make it like so:
Statistics would be Strength, Dexterity, Constitution, Wisdom, Intelligence, and Charisma, as normal.
Races would be Namekian, Human, Saiyan, Hengeyokai (from OA, all the animal people) and the various hybrids.
Classes would be Fighter (Physical combat skill based, for unarmed and weapons), Monk (Introspection and meditation to enhance the power of Ki and perception of the environment), Tech (based around the use of powerful devices to thwart your enemies and gain info - I.E., Bulma), Sorceror (heavily altered from Dungeons and Dragons and based around non-destructive magic - I.E., Bavidi.) and Sensei (Based around instructing lesser warriors and gaining knowledge about your opponent - Roshi, King Kai, or many of the Namekians.) Naturally, multiclassing would be not only allowed but expected, almost vital to survival.
NPC classes would be limited to Commoner, but the DM would be encouraged to allow non-combatant characters (or combatants with no measurable chance of harming the invulnerable PC's) to break the rules in convenient ways.
Prestige Classes would include Saiyan Rager, Kai Disciple, Super Saiyan, Weapon Master, Apocalyptic Warrior (Which is required in order to destroy mountains/cities/continents/planets/solar-systems), Namekian Guardian, and Namekian Mystic. All of them would be offered as both feat chains and prestige classes.
There would be no upper limit on attacks per round, and each would be made at your full attack value, but you'd need to take a feat to gain each additional attack, and the number of feats you could take would be limited.
Energy attacks would be based on feat chains and skills.