Not Updated For Current Season
This is a General idea of a Build i enjoy a ton. It's designed around the burst dps abilities Poppy brings to the battle. Proper use of your Ult will allow you to Even a fight quickly, or tilt the tides in your favor by simply disrupting the opposing group while dropping a caster/carry in VERY short order. Many have accused me of Kill stealing, when in fact, i drop said Champion from half HP with a single flurry.
First Blood for you or your laning partner is easy with a proper stun.
Devastating Blow is your main DPS ability, try to have the cooldown under 3 seconds by the time you hit 18.
Paragon is a great ability to get out of the fray of battle, as well as into it to set up your charge.
Charge is often used in "Limited" functions, such as engaging the fight itself, or chasing. I stress the bonuses that come by using it properly to slam into a wall.
Diplomatic Immunity- I use this to not only help my damage to the target, but to allow me to focus that target without getting wasted by the other DPS in the mean time. Often times I'll pop this shortly before charge, and let the DPS blow my shield up as i walk right through them to my target. Often you will find dps trying to kill you, and your dps is opening up on them in return.
Note: DI is also great for escape situations if you get jumped, Pop it onto the farthest melee or the lowest DPS in the area, and flee.
The Runes I pick are to Maximize the burst dps of Poppy, You can swap out the Defense Runes for other abililty/Cooldown if you choose, though I Select armor for one simple purpose, I love to eat casters. While using my Ult, and a proper charge into a wall, followed by a devastating blow or 2, my target will drop, leaving me exposed to (Most likely) more physical dmg than magical dmg as i make my escape using Paragon
Again, My masteries and Items are based around the damage that my Devastating Blow will do. Cooldown reduction and enough health to survive, while blowing an opponent up. I pick mana early, as Poppy is a bit mana intensive if you get into an early scrim, though Mana Regen tends to not pay out as much in the end, as you only use your skills when you have set up for a proper charge typically.
Early Charge = First blood. With a smart laning partner, and an opponent who decides to hide in bushes, this makes for a great chance.
Many will question my choice on Summoner Spells, mainly Clairvoyance. The reason I pick this is simple. People like to hide in bushes and gank. Near the bushes, are walls. Pop Clair on them, Charge, Devastating Blow, and enjoy the free kill (Especially if they are nursing their wounds already)
All in all, Poppy is a great Hero due to her ability to play so many Roles, This one being my favorite. Pay attention to who you are able to get angles on, and be sure to use all your cooldowns as they pop up, even if it's only to re-Charge. Use the bushes to your advantage, not by hiding in them, but allowing your enemy to, then Clairvoyance/Charge/Dev Blow them to show them why they shouldn't hide there. Feel free to leave any questions, or info in tactful ways, trolls will be ignored :D Best of luck to you and your hunt!