While you're still up here, I do have to mention that at least one part of the build is not quite mandatory and it's skill points can be spent into other skill for your own play style, leaving room for your own customization and variation of said build.

It's the tripmine section.

Always have more options for more peoples to enjoy your show.

Now for what you came for. Pretty straightforward.

Mastermind Tree


What really matters is the extra stability on your weapons. You may need it in extreme firefights.

Enforcer Tree


The Engineer is someone practical, so he uses practical, efficient and simple weapons: the Shotgun.
Reload speed and weapon damage is important, especially in Death Wish to quickly dispatch enemies. Killing an enemy with a shotgun will activate Overkill, which will buff your shotgun damage and everyother source of damage if the skill is aced by 75%. Stacking with the 15% damage buff from Underdog if activated, resulting to a 90% buff total, almost doubling your weapon's damage.

Meanwhile, his armor skills will keep you alive in the fight longer.

Technician Tree


The whole breacher tree can be wiped off and re-spent into other skills you think are more useful for your play style, like sentries, medibags or ammo bags.
Meanwhile, I personally like Trip Mines and Breaching Charges to help my team advance without cops advancing on us.

Using Sensor Mines in aggresive choke points will help you be more aware and ready for any special unit that is coming out of a corner or spawn point without any bad surprise on your end. If all hell breaks loose, you can always change back your Sensors into actual Trip Mines or simply shoot them for the blast and the Fire Zoning.

Let's not forget Steady Grip, for that extra Accuracy and Stability on any weapon, really useful for my weapon of choice.

Ghost Tree


Nothing too special about this tree. Spinter and Second Wind to get yourself out of hot situations. Really great when you need to reload or regen your armor.

Fugitive Tree


The second main part of this build, because it contains most of the DPS to make you aggresively deadly.

Your sidearm being relatively simple as well is a pistol. Quick, efficient, and can deal enough basic damage. With all the pistol skills (Akimbo Excluded), you can turn your small side arm into an heavy caliber.

15 Points of extra damage raw on any pistol gets you good firepower to kill any enemy on Death Wish quite fast. You can up your total damage by up to 80% with Trigger Happy, with each of your pistol hits boosting your damage by 20% up to four (4) times.

Perk deck and Armor

I think any perk deck should work fine with this, but I personally recommend Infilitrator, Crook/Armorer depending on the armor you choose, Muscle... Hell, there's like 10 of those now. Go nuts and choose whatever the hell you want.

For armor tho, I recommend Heavy Balistic Vest and Higher.

You now have the skills, now let me explain to you how this build works.

The Enforcer and Fugitive damage buff skills can stack in a certain manner.

Overkill can stack with Underdog and Trigger Happy to make Pistols stronger, while Trigger Happy does NOT buff shotguns (Until otherwise proven.)

Now stick with me for a little bit of math.

If you encounter three (3) enemies or more, Underdog will activate, buffing your overall damage by 15%. Killing an enemy with a shotgun will buff you by 75% more damage, resulting in 90% Damage buff if you still encounter more than three enemies.

The Overkill buff lasts for 20 seconds, so you can swap to your pistol and land four shots on some poor cops, each of them giving you 20% damage buff, so 80% total with Trigger Happy. You're still following? Well here's some math for you.

15% + 75% + 80% = 170%

That's right. In a heated firefight, you can get a total buff of 170% to your pistol.

Let's take my favorite pistol: the STRYK Full-Auto Pistol. With all the skills, the Stryk becomes the fastest firearm in the game (Excluding flamerthrower) at more than 1000 RPM.

With the raw +15 Damage boost skill in fugitive, it gets an average of 50 Damage per shot.

Still listening? Have some more maths.

What is 170% of 50 points?

85 Points.

That's right. Your Stryk Pistol gets an extra 85 POINTS of damage.

85 + 50 = 135.

That is almost the damage of a single Deagle/Revolver shot.

With skills and proper weapon modding, your Stryk becomes a 37 Bullet-in-mag pistol dealing 135 points of damage.

As intended, you need a Shotgun and Pistol to make this build work. So here are my personal favorites.

Shotgun: The M1014


Mods:
King's Crown Compensator
Long Barrel
Solid Stock
Sight of your chosing
000 Buckshots or Flechettes. But choose any ammo type, realy.

Pistol: STRYK 18c


Mods:
Ventilated Compensator
Polymer Flashlight
Laser Grip
Extended Mag
Stock
Pistol Red Dot Sight

But of course, use any weapons of your choosing. I'm just an engineer, not weapon specialist.

TL;DR
Shoot face with shotgun, take pistol, shoot more face with pistol
Rinse and repeat.

I cannot STRESS this enough. If you do not like Trip Mines, PLEASE just change it for whatever the hell you want.

Meanwhile, this was my first build guide. I hope you enjoy your experience with my build