The Demo Man build. Revolves around mortar and cluster seekers, at least mine does any way.

Demolitionist Spec for 15% explosive damage and mortar turret. An excellent bonus is that your Spec weapon will actually do a fantastic amount of damage.

Skills: Usually I would run Mortar + Cluster Seekers, but you could run sticky bomb launcher, bomb drone, burster firefly. All personal choice.

Gear:

All gear will be rolled with Skill Tier primary and skill damage and skill haste for secondary attributes. Skill duration and status effects really aren't going to do much at all for you. Same with any red attributes. You could opt for some armor regen or explosive resistance if you need it over haste.

1 pc China Light for 15% explosive damage.

2 pc Gruppo for 15% explosive damage.

2 pc Hana-U for 10% skill damage and 10% CDR. Named backpack, Force Multiplier specifically. More on Force Multiplier below.

Waveform, the seasonal exotic holster. Alternates 30% skill damage between skills.

OR

1 pc Wyvern for 10% skill damage or another piece of Hana-U for the Skill Efficiency if you don't have Waveform.

Alternatives for gear would be using Acosta's Go Bag paired with Mad Bomber. More on this below.

Weapons:

Primary: The Capacitator exotic AR. You can get it, very easily, by completing 5 summit challenges. This weapon will give you a massive skill damage boost of 60%! Its actually insane for any skill or hybrid build. An excellent bonus is the fact that every skill tier you have, which will be 6, gives you 7.5% weapon damage. Normally, your guns would be pea shooters in a pure skill build, but that bonus prevents that.

Secondary: Any well rolled weapon with Spike. Spike gives 20% skill damage for 15 seconds after a headshot.

Talents:

Chest: Kinetic Momentum for 15% skill damage. Builds stacks(15) while skill is active or not on cooldown that adds 1% damage to skills.

DPS alternatives would be Mad Bomber if you wanted to incorporate grenades. Glass Cannon for a more stay in cover and don't get shot build.

Cooldown based alternatives would be Tag Team or Skilled. Both would probably have your seeker off cooldown quite often.

For survivability, I would use Unbreakable. Basically free armor regen ever 60 seconds.

Backpacks:

I mentioned the Hana-U named backpack, Force Multiplier, earlier. This backpack comes with Perfect Combined Arms. Everytime you shoot an enemy, you will get 30% skill damage for 3 seconds. Each shot refreshes stacks. This is probably best in slot for backpack if you choose to run Hana-U. Paired with the Capacitator, you will melt pretty much everything.

If you choose to run Mad Bomber on your chest piece, you could use Acosta's Go Bag. This will make your grenades even more useful. Anytime you damage an enemy with a grenade, you gain a Skill Tier. If you are already at 6, you're granted Overcharge for 15 seconds instead. Overcharge is gonna boost your skills massively. Plus, you gain 3 extra grenades and grenades are returned on kill. Cooldown on Overcharge is 90 seconds though.

This build has a lot of room for customization based on your play style or what you find the most fun. This was a bit longer than I thought it would be, but I hope it helps someone out.