I feel that Shaco is a very punishing champion in that you need to really take advantage of his strong early game to stay relevant. Getting good ganks off early could be the difference between getting yourself and the team to snowball, or just not being able to do much where you can't burst people down and get cc'ed and killed instantly in team fights (whereas if you are fed, you can split push and have a lot more options).
Problem with manamune is that it starts with 720 gold for Tear that does not offer combat effectiveness, and takes a long time to charge up. With how important the early to mid game is before the other team starts grouping up, For around the same price, you could be well on your way to working on Ravenous Hydra, Statikk Shiv, or maybe even Blade of the Ruined King. Since your first auto when coming out of stealth is guaranteed a critical strike, you will want to build AD and some Attack speed to finish off targets after the initial burst after you slow them with Red / using your E.
He just works so well in the jungle due to his fast and safe clears with boxes, as well as strong counter-jungling and ganking potential. It just feels like his kit is not as well suited to laning. I feel that Shaco is strong in skirmishes of 2 vs 1, 3 vs 2, etc, but less so when there are more people unless you get a really good flank off on the other team's carries. Since he tends to be built glass canon, you have high damage, but will have to get really close to your enemies. In laning phase this will not be a problem since there are only a few people there. Getting Red, using Q to sneak in, and chances are you can get the kill since it will be difficult to escape the Red buff slow and your E. But, in team fights, you can get bursted down almost instantly when you go in. After laning phase and if they are grouped up, it's usually better for you to just split push with Shaco since you are still a strong duelist and has strong pushing potential as well as the ability to escape if they send multiple people to try to get you.
In the jungle, Shaco is strong in his mobility, and high bust damage + sticking power. He can pull off some really strong ganks that will snowball you and your team mate(s).
in terms of laning, it will depend on how well your lane opponent understands playing against Shaco. It seems like he would have strong zone control with the boxes that can make ganks difficult for the other team, and potentially for the enemy laner to go into certain areas. Shaco can probably apply quite a bit of lane pressure, but, at the same time, it can be harder to get kills and snowball if your lane opponent just plays it safe and out scale you.
In top lane, chances are they will not want to push lane against you since it will be difficult for them to escape, but at the same time, you can only really gank mid / take top half of jungle. It makes you more predictable, and you will have less chance to snowball.
in mid, Shaco will be able to roam top or bot where you can apply a lot more pressure. But, downside is that you might get stuck farming mid against champions that can wave clear well where.
Instead of getting more mana in that crucial early to mid game period (by late game, chances are you will not be able to finish charging the item), it's probably far better to build more damage and make every ability count. In terms of damage, you take huge dip when you pick up Tear without being able to finish Manamune. But when fully stacked, you get at least 45 AD + AD based on mana + toggle. But, say instead of 2200 for Manamune, you get a Tiamat for 1900 gold, you immediately get more AD, clearing power, and burst with the active. And you will be able to eventually upgade it to Ravenous Hydra gives you 75 AD and a lot of other nice effects. Similarly, you could have picked up BilgeWater cutlass (for that Blade of the Ruined King that will really increase your dueling potential with the heal + slow, and the % health damage) + some other items, or maybe even a BF Sword for a huge 45 AD boost. With the immediate boost in AD, you can take advantage of that window of time when you can get ganks off that can snowball the team. And even Zeal + Avarice Blade will be really good after getting your first AD item.
I just don't think it will be worth it, where it's probably far better to go for items that immediately give you an advantage early on in the game to take advantage of Shaco's brief window of power. There are just so many better items.
