Build Specs and Cost- ~$600:
Cujo 20" Plus Bike - $440
Spawn 127mm Cranks - $65
Shimano 395 Hydro Brakes - $70
Shimano UN55 BB - $20
Stans Schrader Tubeless Valves - $16
Sram X9 10 speed - $0 (Old takeoffs)
ESI Grips - $0 (Old takeoffs)
21.5 lbs on the scale with pedals
I originally planned to build up a Gary Fisher 20" for my son that is real similar to a Trek Pre-caliber. I was going to do the Suntour 20" air fork, spawn tubeless wheels / tires, plus the other upgrades I did here, but a few things pushed me in this direction. The cost was nearly the same and the GF was going to be heavier, but the biggest factor was watching big sister ride a 24" Plus Specialized RipRock and roll right over roots on a few uphills that were hanging him up on the Gary Fisher. The plus tires swallowed up the roots for her at slow speed and stopped him dead in his tracks.
One thing pretty cool is the Cannondale comes with a 7speed Freehub which let me upgrade the drivetrain without swapping a hub. You can fit 9 of the cogs from a 10 speed setup and adjust the limits to work fine.
In my opinion the Shimano hydros are a no brainer upgrade and the new BB was a recommendation from the shop that I never considered about but for 20 bucks seemed like a good call. Wheels setup tubeless no problem and we are running them at 10 psi. I cut the chewed up end off my grips and put them on the kids' bike and they all like the little bit of extra cushion from the ESI's
First ride we knocked out 5 miles of trail in 45 min and he noticed immediately he could ride up things he couldn't before. Downhill he never had much issue before since the speed was there and he just bounced right over everything.