Build him as a carry. (no really)
After a generic blink/guinsoo's throw in skadi/mjoll which is always the favorite caster combo and a buriza. If you can farm all of that gold you won't fall off at all, the ability to constantly chase someone with that much auto attack damage will keep you extremely relevant if you play properly. Puck can easily gun down some pretty tough heroes just by being able to constantly dodge and blink around. Imagine a fed SB who can't do anything because every time he gets next to Puck, Puck just phase/blinks away and keeps attacking him until he's dead.
Of course, you might say "anyone is good with those items," but again, if the game is over at blink I don't see why he needs to be relevant late game, the game is already over. Most games are over in 30 minutes and his spells are still pretty relevant. As much as any other int hero, anyway. Compare him to Lion who does waaaaaaaaaay less damage in a team fight. Two very reliable CCs, yes, but that's the trade you get to make as an int hero > CC for damage. If you have a Dark Seer to vac everyone together, Puck by himself can hit two thousand damage with his two basic spells, that's pretty neat. Lina does more, but Lina doesn't have Dream Coil or phase, either.
I personally don't like Puck because I just can't stand his early game. Cower at the tower and shoot off Illu orbs to try to scrape together enough last hits for energy boots so that you can start spamming creep waves for blink so that you can FINALLY be useful beyond ult>die. Talk about your crappy auto attacks from a hero with pretty much zero lane presence.