I like builds that are at least a bit tanky. As I'm playng games with lots of lame players because of my low elo, it is quite good to be able to tank a bit instead of our tank which is trolling somewhere in the jungle while everybody else is in teamfight.
Most items in this build will give your Jayce something useful for defense and at the same time for offense. Output dmg is not very high, but if you realize how long you can stay in battle, it is VERY HIGH at the end.
- Initiate with accelerated Shotblast and accelerate yourself by running through it.
- Convert to Mercury Hammer and attack enemy by Q, and then pull him back by E and retreat a bit.
- Swich to canon and haras and wait for oportunity to do this again.
- If you want to kll enemy, after Q turn on W, run behind him and pull him to your side by E and kill him.
- If he run, swich to cannon to harrass or last shot him.
- Phage and BF Sword at the beggining gives you enough dmg to farm efectively and also to kill anybody. That gives you time to build some more early tankyness - you already have some from Phage.
- Mercurys gives you mobility and some basical resist for most of the game, Giant belt gives you goot base for withstanding all types of damage and to make diving possible.
- From Trinity you will start to improve your damage at the first place. You are not tank, you just want to survive to kill. Trinity gives you some damage and very needed atack speed, but also some more tankyness: lifesteal and health and manapool.
- It is not very expensive to impoove yout Giant to Sunfire, so why not to do it now. Sunfire passive stack very well with your lightning field and thaks to this you will deal a lots of AOE to anybody near you.
- You already have BF Sword so it is no problem to upgrade it to Bloodthrister. And again you will gain tankyness - lifesteal. You will enjoy jumping on enemies and burning them with your sunfire/lightning field combo so there is nothing better than to steal some life from them while fighting with hammer.
- You would like to use your ranged atacks a lot and for this you would need more attack speed. This is time to start building Madreds but for now it will be enough to get speed from Recuvre bow. Faster lifesteal, more harrasing from ranged autoatacks.
- Your problem now are probably AP enemies. Lets start building Maw. Great for sustaining, resisting and also improving damage at the same time. Hexdrinker base will be enough now.
- Your damage is a bit too low to damage tanks efectively so lets finish Madreds to counter Warmogs. If you are having problems with heavy armoured tanks, get last Whisper instead of less needed item.
- And now finally finish Maw.