I was torn between buying an E-mtb or building my own.  Since I already owned four hardtails, I figured it would make more sense to convert one instead of adding another bike to the stable.   This is a medium NS Surge Evo frame set, 750W BBS02, 48V 20aH triangle pack, 130mm Fox Rhythm 34, 27.5" Stan's Flow rear wheel with E-Sync freehub, 27.5 x 2.6" Kenda Regolith Pro rear, Nevegal 2 Pro front (both EMC casing), Deore derailleur with a Saint 10-speed shift lever and 10-speed Microshift Advent X 11-48T cassette.  170mm x 30.9mm PNW Range dropper, Spank 60R handlebar, Spank Spoon Stem, Raceface Aeffect-R pedals.   

Future upgrades will be a matching Stans's flow front wheel, Samox 160mm crank arms, and possibly a beefier/longer travel fork.  

This bike absolutely rips!  I have already put 35 miles on it in the first week, a mix of pavement, gravel, and singletrack.  It has plenty of torque and climbs like a goat with the 48T largest cog.    I am pumped to be able to hit the trails and climb without getting gassed out in the first half hour.  I am really glad I went the DIY route because now I can maintain everything myself.  

if you're on the fence about buying vs building and have some experience with bike building and basic mechanical/technical skills, DO IT!!  The feeling of riding something you build yourself from the frame up is so damn rewarding!

My DIY 750W BBS02 Mid Drive Build, based on a NS Surge Evo frame, I call it the "Surge E-Volt"!