So I decided a lightweight build would be fun. Here's the result:

With a red dot, light, and loaded 20 round magazine...weight is 6 lbs, 8 oz. It gets up to 6 lbs, 12 oz with a loaded 30.
Didn't take a picture of the loaded weight with the 20, but here it is with a 30 round magazine:

I've shot a lot of ARs from 10.5" to 20" and everything in between. This one is by far my favorite that I've ever owned or built. Could have made it even lighter with a 10" rail instead of 13", skipping some ambi parts, going with V7 titanium bits, etc....but for close to the price of standard parts, this one came out pretty well I think.
Parts list and reasoning:
Faxon 14.5" pencil barrel, midlength gas with a Voodoo Manimal pinned and welded to take the gun to 16". Lightweight, Faxon has a great reputation
ALG EMR V2 rail. Light, Mlok compatible, comes with QD points on either side, free floats the barrel. Great rail, and light.
.650 low pro gas block. Could have saved some weight here by springing for one of the LW options, but...$$$$$.
Areo Upper w/no forward assist. Another easy way to shed a few ounces.
AIM Surplus Lightweight BCG. This thing shaves 3.9 oz off the regular BCG and doesn't cost an arm and a light. Very happy with it.
BCM Ambi Gunfighter charging handle. I'm a lefty, decided not to save weight and go with ambi parts here.
Standard PSA lower. Could have saved weight and bought a LW lower too, but like the gas block....a place I chose to save $$$$.
Magpul K2 grip. Light, slim, no finger grooves.
Geissele SSA-E. This trigger is amazing. If you've never shot a Geissele trigger you don't know what you're missing.
CMMG Ambi safety. Another stop where I cared more about function than weight savings. Stupid dominant left eye.
Spikes T2 buffer kit. Wanted a good buffer set up to pair with LW bolt.
MFT Minimalist stock. Light weight, has QD point for sling, tight lockup.
Primary Arms Advanced Red Dot. Light weight, not too expensive, good battery life.
ScalarWorks QD mount for red dot. This thing is awesome. Super light, easy to take on and off, locks up tight. Great mount.
TLR-1 HL light. Already had it, and they're fairly light and familiar to me.
6 1/2 pounds loaded is nice. I think I've found my new home defense rifle. Plan on shooting it at Cola Warrior this year with a 5x prism, but its a little heavier with that optic on it. Red dot will serve nicely for most days.