I know that this issue is present for every player of league of legends, and it's very annoying.
Many, if not every match that I play there's more than one person that wants to be either mid, adc, top, jungler or support, and this in most of cases is just decided by who "picks first" as the "player made rules" set it. But sometimes somebody just wants to play that champion and locks in, so the other person who called it first also locks in because it was their right to play with it, and this causes a trouble for the rest of the team, making them in most of cases, lose.

I came up with a good idea, and I really think it should be considered because it will prevent that problem every time. (unless it's a troll who just wants to make you lose to have fun, no matter what champion they use).
It is a system for the queue that before you start getting matched, you chose what you will play. Of course this will just work for the normal META and there could be a "free pick" queue too, just like it is now.

In this, say somebody picks adc, then the system stops counting every other person who picked adc to match them with, and this is done until adc, top, jungle, support, mid are picked.
For this to work, every champion would have to be classified as whatever it is, and if somebody chose support, they would just be able to pick the support champions. This goes for every other champion class.
Maybe just enable this for level 30, since at lower levels everybody choses what they want.

Please comment your opinions! I really think this would change the gameplay.

so you want to make a whole new queue system? and have different rankings for this new system? or just a new match making system similar to the one found in WoW?

I don't play WoW and no, no new ranking system, just make it for the Normal matches, but instead of everybody chosing anything, before they get matched they chose what role they will play so there's a META team formed in the matching, there would be 1 support, 1 adc, 1 mid, 1 top, 1 jungler. Every person of the team, before getting matches chose their role, and with that they were matched with the respective team. This way, the role they pick allows them to just use the champions classified as the rolse they picked.