Gideon remains the character I've had most success with on Pred. He has good mobility and burst potential, but most importantly - his ult turns the tide of fights.
My bruiser build focusses around his Black Hole ultimate, being able to put yourself in the air to provide you team much needed backup. What you will find, if you're used to building full mage, is that you don't have masses of mana, so being frugal with abilities when laning and taking ownership of the river buffs is important.
Focus early on last hits, and avoid running dry on Mana. You should be rotating to fights a lot throughout the game, but ideally you want to make it to level 6 as soon as you can.
So, the core build is below - I flex a LOT based on the game, so I've included a number of key options and explanations below it:
Crest: Occult > Tempest
Use this when you ult over a big fight and the additional damage and sustain is insane.
Dreambinder
My non-negotiable start item. Slows enemies damage by your abilities and does more damage to slowed enemies. Only way out of your ult now is with a blink or long movement ability Also power and health is the base of our build.
Astral Catalyst
It is not uncommon for 2+ people to die after you ult in a fight, which means your ult now has a big cooldown reduction. Early game, this is huge. You also get some mana here, which gives you a bit more to play with.
Lifebinder
Since the update, this now gives Ability Haste based on power. It also gives you additional power from a takedown. This really helps clean up after your ult.
World Breaker
Power based on your max health (Somewhere around the 60 mark), plus a scaling boost each time you deal magical damage. Your ult ticks multiple times, so follow up abilities will benefit from it.
Flux Matrix
It's rare that I get this far in a build, but Flux Matrix seems like good synergy. More health (and thus damage) and deal additional damage to enemies around you, seem pretty decent to me.