GrimTools: Warlord, Level 100 (GD 1.1.9.7) - Grim Dawn Build Calculator
Here is a 47% cooldown reduction build. This works in conjunction with Time Dilation (which has its cooldown lowered), which reduces active cooldowns by -6s each time. I was mainly looking into this build to see if I could basically have Menhir’s Will almost always ready to go whenever you needed it, with a bunch of other buffs that supported it… The idea being, of course, creating a nearly unkillable character by virtue of Menhir’s Will always just about fully healing you (with enough healing effects increased) each time, and being off cooldown by the time it needs to go again. While that specific goal could be more directly optimised, here’s a first draft build of a lowcooldown tanky caster using a whole bunch of temp buffs.
Affected buffs and skills of note include:
- Time dilation: 8.48s
- Twin Fangs: 0.318s (0s with Time Dilation)
- Ascension: 12.72s (6.7s with 1 Time Dilation, 0.72s with Time Dilation x2)
- Overguard: 12.72s (6.7s with 1 Time Dilation, 0.72s with Time Dilation x2)
- Arcane Barrier: 1.59s (0s with Time Dilation)
- Turtle Shell: 4.24s (0s with Time Dilation)
- Resilience: 7.95s (1.95s with Time Dilation)
- Menhir’s Will: 7.95s (1.95s with Time Dilation)
- Fighting Spirit: 6.36s (0.36s with Time Dilation)
Ascension and Overguard’s cooldowns last long enough for Time Dilation to be cast twice during that time, potentially allowing their cooldowns to be reduced to ~6.7s with one Time Dilation, or 0.7s with two Time Dilation casts. Of course, the timing of Time Dilation is not assured and rarely would it be perfectly optimal. But, it’s still not bad, right? 
Watching this video, you can see how rapidly things like Arcane Barrier, look for the purple buff in the buff list above the HP bar.
Vid Demo - A bit of chunk 3 and 4 in SR. This was a first attempt at running the build; there is no time left on the clock as I was stubbornly testing it’s tankiness.
The build is not optimised, and requires a green shield with one of the two Cooldown-providing prefixes. The medal could be swapped out to give extra 2s resilience and a 12% heal with every cast of Overguard which isn’t bad! What would make this build significantly tankier is the use of Menhir’s Bastion, as this build currently has no % damage absorption. Also, Stone Form with cooldown this low would basically be permanently on, making for a very tanky experience. But, if I did those things, the damage would be even lower than it already is 
Enjoy!