First off... this is not a joke build. I have seen some move speed Janna builds that are just jokes to see how fast you can possibly move. This build is based on speed, but is actually very effective.

Imagine this scenario: you are in top lane farming away when all of the sudden you mid carry is getting ganked from the bottom. You ping telling the carry to come towards you, slap on ghost and are across the map in 2 seconds. By this time your carry has 1/4 life left, so you put your shield on them and throw out a tornado to knock up the pursuers. Then BAM, all of the sudden morg jumps out of the jungle and snares/ults you. No problem, use cleanse and your ult to push her away. Catch up with the carry and trigger Shurelia's to give you the boost you need to make it to safety.

This build will likely get you no kills, though I have gone 9/1/20 with her as well. The focus of this build is on assisting kills and enabling escapes. Your outrageous speed and mobility will make you a huge asset to your team because you can get anywhere on the map in time to save or enable.

Ghost is an absolute must on this build. You will already move faster than anyone else in the game, but when you pop on ghost, you can cross the entire map in a matter of seconds. This is the make or break skill for catching up to teammates in time to save them or enable their kill.

I like to use Cleanse as the second skill, but this can also be substituted for teleport. Cleanse is great because enemies will often target you (the squishy one) when you pop up during team fights. This will help you break free from cc effects and keep doing your job.

The runes are somewhat arbitrary. Definitely go with health or speed quints for obvious reasons. Cool down reduction helps a lot with Janna as well, because the more often you can use your skills in team situations, the more useful you will be. Other than that, you can go with mana or ap or magic pen... doesn't matter too much.

The item build is central for this Janna. Your skills will not be very strong, but that is okay. The point of this build is not to have a strong tornado that will damage enemies or a shield that will allow you to topple towers, but instead all of your skills will be used for escapes or enabling.

You can substitute in mobility boots for the speed boots if you want a little extra speed between lanes, but I prefer boots of speed because you remain very fast during team fights, while you have to wait 5 seconds after fighting for the boost to kick in on the mobility boots.

Force of Nature is an awesome item. Not only does it give you a nice speed boost, but the health regeneration and magic resist help a ton as well. I find that my health often regenerates to full as I make my way across the map to help out a teammate.

Shurelia's Reverie serves a couple purposes. You get a nice bit of cooldown reduction from the kindlegem as well as good health and mana regen. The best part is the active effect, which when triggered allows you and your allies that are close to you to move more quickly for a few seconds. This helps SO much when you are helping someone escape. Run up to them, shield them, knock up the enemies with tornado and then pop the active and you can both speed out of there safely.

Lich Bane is the next item. This one is pretty obvious. A great mage item with even more movement speed.

This build is somewhat expensive, but so far, I have been able to get all of my items in every 5v5 that I have used this build. After Lich Bane, just use your discretion and try to get something that makes sense for your team.

The play style on this build is pretty obvious, so I didn't feel the need to break it down step by step. Just be sure to focus on what is happening on all parts of the map, and make it clear to your team what your role is so that they know to run towards you when they get into trouble. You will be the silent hero of your team.

Finally, I would like to say: don't knock it 'til you try it. Please give this build a shot before rating it. You might be pleasantly surprised.

Thanks for taking the time to read my first guide. Try it out and let me know how it works out for you!

ps: I may add to this later, so questions/clarifications are welcome.