An idea: Have some very useful or overpowered items that don't fit in the campaign in the most random places, but can only be obtained with a perception roll of 20+. These can be used in home-brews and act as super secret items. They wouldn't be necessary to complete the campaign but add a huge random factors into a game, like a magic quiz orb where if the finder can answer all the trivia questions they could get one powerful item to keep. These secrets would be littered around a campaign but in the oddest places such as a dumpster or under the 15th table in the bar. These will encourage the player to explore and find these secret items maybe even having a secret ending for collecting them all? What do you think of this idea? Is it an okay or interesting premise to add to a home-brew game? Or is it just an unusable idea that would break the game completely?

Depends on your level of pain with players asking to investigate... look at... examine... fondle... scrutinize, etc every single living blasted piece of environmental riff raff trash that you hadn't even thought of putting in your world yet just to see if it holds a Magic Ring of Everlasting Life.  If you are ok with spending hours and hours and hours rolling for this stuff in every campaign, go for it.  I prefer to use the Powerful Homebrew items as quest or NPC favor rewards.  They don't waste their (and your) time dumpster diving through their nightly bar crawl hoping to hit the Legendary Lottery.  But... if they hit it... they'll enjoy the heck out of it and will never stop even when you have campaigns without the crackerjack box prizes.

Personally I think this would slow down gameplay because it encourages players to look under every single stone they encounter. It also has a decent risk of creating huge differences in the power levels of your PCs, which can frustrate players. It's just not fun to be the rogue, when the monk can do everything you're specialized in but does it better.

If you want to use this, I would try to stick to "limited use" items, like scrolls, wands, potions, etc.

Thats a good point, I guess depending on how hard it is to find that would heavily slow down the game since everyone will be looking for it.

I do that in my games. There's really nice items scattered in the world but they all have a reason. 

In your example, under or in a dumpster, I'd have the item in a package with a note. Making it a secret delivery that the players stumbled across. After that the people that delivered it and went to get it would actively start looking for the people that took it. I'd have someone watching the drop off point from a distance to report what happened. The reason that person didn't confront the players at the time was that they were out numbered. 

So it can be done. Just have too think it all through. 

Personally, I prefer magic items to be rare enough that you're not going to trip over a random vorpal breadknife in the cutlery drawer or the like.  Simulating the "hide cool items in inexplicable places for no reason" aspect of many video games does not make for all that good of gameplay in a tabletop game, IMO.