Let me preface - Im very new and just started building my fist multi-rotor, but have some experience with planes and have equipment that can be used with the mult-rotor build (that cuts my cost down).
Heres how I attacked my build...
1. Set a Budget (and plan to go over it, a little).
2. Are you wanting some to practice with? I purchased a $40 quad from amazon that got me the basic flight controls
3. Know your skill level? Plan accordingly, can you solder?
3. What kind of flight Controller do you want? Do you want plug-n-play out of the box (naza), basic functions (multiwii, kk2), full auto-pilot (APM 2.5)?
4. What kind of payload do you want? (camera only, gimbal and camera).
5. What type of frame do you want?
6. What kind of flight time do you want? - this will determine your battery cost
7. Plan for spare parts....stuff will break (at least thats what Ive learned with planes).
Im constantly shifting my funds around to fit my purpose and stay within my budget.
With all that said...I've seen some pretty good builds out there. The flitetest.com multi-rotors look pretty cool and I would like to build one later on down the line....Ive build two other there scratch build planes and had no regrets.