This build requires a few DLCs, some required some optional some highly advised
Sokol Pack (Grinder, required)
Wolf Pack (China Puff, highly advised)
Gage Assualt Pack (GL40, highly advised)
Butchers BBQ Pack (Molotovs, highly advised)
Golden Grin Casino (Buzzer, there is a free version but some prefer the way the Buzzer looks, optional)
Of course other than DLC you need a few in-game milestones to have this build work
Infamy II+ (Choose Fugitive perk for this build)
Level 100

Basic Joker and hostage skills, the extra health regen from Hostage Taker is useful for when your turrets aren't killing anyone and Jokers always help deal out more damage.

Resilience aced to help with the pesky flashbangs Die hard basic for helping with fixing drills and transporter basic to move bags faster.

This is where you spend the majority of your points, ace everything in the engineer tree, this will get you the maximum amount of maximum upgraded sentries.

Your basic movement skills, no really thats it.

Some basic One Down necessities here, Nine Lives aced for that extra down, swan song basic, I would get aced but this build is a little bit too point heavy for it, Feign Death aced so that if you go down you have a 30% chance to get back up, and Messiah aced so that if that 30% fails and your either going solo or your teams stuck you can get yourself up.

For Primary I reccomend you use the GL40 as with Turrets the grenade launchers will actually get you the most turrets as they only take one grenade per turret, and if you pick your turrets up before they completely run dry (even if they have 1% ammo) that grenade will be returned, it is not reccomended you actually use this unless your downed and need to use Messiah.

For the secondary the China Puff is the best option, everything I said for the GL40 goes for this as well, if you don't happen to own this or the GL40 any weapon will do its just that these are the best ones, try to use ones that you can avoid firing so that you will always have ammo to refill your sentries.

Do I even need to explain this? It was in the title. But for those of you that need it, Grinder is a perk deck that allows you to heal on damage done, this counts for Sentry damage as well so for each of your 6 sentries firing you will be gaining health for every point of damage every 1.5 seconds.

The Lightweight Ballistic Vest is the best armor as we don't have any dodge so the slight boost in armor is more useful to this build.

Molotovs are the best throwable as they blanket an area in fire, and for each fire damage in 1.5 seconds, you guessed it, you heal. The free incendiary grenade could also be used but it just ignited enemies nearby rather than leaving an AoE of fire.

The Buzzer is the best weapon for this as it stuns enemies, the Electric Brass Knuckles does this faster but as far as I can tell the Buzzer swings slightly faster, use whichever you prefer. The stun is most useful for dominating cops to make Jokers as you can stun them and then dominate them while they're stunned.

Use Jack of all Trades to bring 4 silenced sentries and 2 normal ones, place them around and make sure they all have ammo at all times, try to get your Jokers and a few hostages for health regen and so the Jokers could do more damage on top of your sentries, don't ever actually fire your grenade launchers but rather wait for you to go down and use them in Messiah as that ammo is more useful refilling your sentries.

This was my first guide, and the first build I felt was good enough to share, so I hope this helps you with One Down heists, its certainly helped me already.