Pros:
- Q and W provide heavy utility with or without high AP.
- Ult is true damage.
- Both physical and magic damage on every auto.
- A bit of natural tankiness from ult.
- Good amount of lane sustain.
Cons:
- Melee.
- No mobility or instant gapcloser.
- Only decent sticking power, Rylai's required.
- No defensive steroids/shields/healing in battle.
The pros are pretty dandy, but the cons are heavy. You can't auto attack someone to death if you can't both catch up to and stick to them for an extended period of time. Cho can nail someone with Q, creep up, silence them and begin auto attacking, and then he's got to hope slows from the crystal scepter are good enough to hold someone close by. Five years ago, permaslow like that was almost overpowered. However, there's so many blinks and dashes and hops and tumbles in today's League that slow really doesn't mean a whole lot to a good portion of the roster.
Just as well, the champions that can't escape your permaslow would be better off just turning around and kicking your ass. It takes time to get off autos even with a good amount of attack speed, and that's time the opponent can use to blow you right up. You do get some HP from your ult, but it's not guaranteed to be there all the time. If you can't live to auto attack enough, you won't be doing much of anything but feeding.
The best solution is to take Cho bot lane as a melee carry with a heavy lockdown support like Leo or Thresh or Naut. They have the CC and the reach to grab someone and hold them until you can catch up and start your attacks. Your natural sustain should help quite a bit in the face of constant poke from the enemy marksman/support as well.
However, if you want to go solo, it's best to go for a more bruiser attack speed Cho. Yes you'll be doing less damage, but you also won't be dead and doing no damage at all if someone decides to focus the giant, squishy cockroach that seems intent on charging into battle. Try to grab items like Wit's End that add both tank stats and enhance autos.
Personally, if I was going to try to make this build work, I'd probably go for a build close to a Morde. Morde loves AP, AD, and tank stats to do lots of mixed damage and stay alive while doing it, and those are things you should be aiming for. Gunblade can give you a bit more healing, Black Cleaver may be worth looking at, Dead Man's Plate could add some speed and damage, Botrk could be something to try out, Maw might be alright just for the passives alone, Titanic Hydra has some synergy with your ult, the Hextech GLP has some promise if Gunblade doesn't work out. Moonflair Spellblade would be godly on it's own, but that's not on SR. If you really want to get crazy, try a Frozen Mallet instead of Rylai's.
If you insist on going full AP autoattack focused Cho, I would grab a Lichbane, a Gunblade, Thunderlords, and a Ludens just to try to do as much up front burst as possible with your first couple autos. Because you're probably not going to live longer than a couple autos, and if you do you want the other guy to be dead ASAP before he can use his mobility to escape.