You don't need the enemy to be roaming. Though preferably not in lane. If the enemy get's chunked down enough that they have to back, that's a good time to roam. Some times when I'm playing a Jungler, if I know my midlaner wants to be roaming, I will gank them first, and often, trying to free them up. If a Jungle gank works, you and the Jungler can easily both go bot, creating a 4v2 which should cause the enemy to insta give if they didn't fall back.
Another trick you might try with the Jungler is if the enemy thinks your roaming, Try and bait a gank. This may require a pick ward in the bot side brush though. (so you have uncontested vision) And that can also free up to roam.
But over all, you really want to try to get some advantage over your lane opponent. If you shove wave into their tower, they can't follow you without losing CS. Similarly, you don't want to roam if your getting pushed in, or you'll lose CS. Personally, I prefer Ahri, since she can quite Easily clear wave, and push in the enemy.
One thing to be careful though, some champion are really good at countering roaming champs. Ones that have similar ability to shove wave, but also have good tower sieging power. (like Jayce, or other AD midlaners) They can easily put pressure on mid, if your gone for too long.
but in the grand scheme of the early game. If you have a relatively balanced matchup in the mid lane, and your opponent is equally skilled. That would almost always end up in a stalemate. And if you want to get ahead that early in the game. You would almost always need Jungle pressure to break the stalemate.
or 
, still learning the basics of this game, not getting much help from friends and such.
Since these two are heavily dependent on roaming, I was wondering what you are supposed to do when your opponent isn't roaming.
It's quite hard to push your minions into their lane if they're not roaming either.
What usually happens is I stay in lane till 20 minutes in game, just farming and poking down the enemy until there is a 3 v 4 in botlane and I leave to help.
Is there anything I can do in the first 15 minutes to get ahead of my enemy?
xoxo
