I think the name is dumb lol but here's a few pointers. k a few more pointers than i thought.
I think the abilities have to be quite generic for them to viable with a variety of builds, but if you use the ult as a role selection... for example, leveling the ult gives you some options, like khaz's ult.
each choice is different. one choice makes the rest of the abilities scale better with ad, one with ap, one makes them ranged if you want that range item etc. BUT! If you want to do that either you have to have the abilities scale a little bit with EVERYTHING to start (ad, ap, max hp, etc) or not scale at all but have higher base values until you choose an ult.
with the passive maybe it could be a bit of extra gold, then each choice of ult changes your passive depending on what you chose.
HOWEVER! i'm not sure it's possible to create a champion like this BECAUSE! i don't really know how to explain it cause it's quite complicated BUT! i'ma try.
maybe one ability can be melee ad based, one can be ranged ap, one can be tanky or something. that would supposedly open the doors for all kinds of builds. mostly i think it would be extremely difficult to create abilities that would sync together in a way that works with each different build.
the only way i see it working well is if each choice of ult changed each ability slightly, so it works in each different way. that might make the champ way too complicated, but these are all just suggestions. also if you want to eventually create a lore for this champ... all i can say is good luck.
hope that gave you a few ideas. good luck with it.
EDIT: i didn't say if it was a worth while idea. HELLZ YEA! and if you manage to do it well, then congrats you're a pro, and the champ should be in league immediately, but i honestly doubt it will be very good. i can help you with numbers and stuff if you want or bounce ideas. just add me in game if you want to give it a shot.