Late update, I won 2 DIY kit in an ebay auction, at 20$ each I had nothing to loose getting them, the last kit I build was in high school, some radio shack radio transmitter, I remember it was super small and had maybe 10 pieces... so it's been a while since I attempted any soldering, I ordered a helping hand kit too to help thing out.
Kit one : AI002 Mixer by AI Synthesis
The AI002 Mixer is an audio or cv mixer. All three inputs have a level control, with full clockwise allowing full volume prior to the summing mixer. The summing mixer is at Unity when at 12’0 Clock, and overdrives as it moves clockwise. This kit is ideal for those who know how to solder, but are still starting out in their DIY Synthesis journey.
It took me about 2 hour in total to assemble, soldering the IC socket and power pin were the hardest part as I used too much solder and contact point would connect with each others. When I first tried it only one of the channel worked so I touched up each solder point a second time and it fixed everything. It took me a little while to realize there were a tiny screw on the knobs... lol.
Kit two: CVpal by Mutable instruments
Cheap and cheerful DIY USB>CV/Gate interface
Entry-level, fool-proof, DIY kit (only 25 parts to assemble)
Plenty of modes (mono CV/Gate/Velocity/Square digital oscillator ; duophonic and dual channel modes ; 4 note trigger conversion ; CC to CV conversion...)
Digital calibration provides better accuracy than offset/scale trimmers
This one was much easier to build I recon doing it in under an hour, getting more comfortable with the soldering and using proper amount without making a mess. Once I powered it up and connected it to my computer Ableton Live wouldn't see it as a midi device, rechecked every connection and went to their website for troubleshooting (one thing I love with those kits is that they are very well documented)... lurking around in the forums I found out some of the IC chips weren't programmed when sent out... I was pretty sure I was gonna need to order a new one until I realized that I had put the IC chip in the wrong direction... once I flipped it all worked :p and while I was digging in the documentation I found out there's actually an oscillator when you use a different midi channel so my box can make sound ;)
Anyway I really enjoyed building the kits and planning to get more.