generalzouIf you're willing to invest in some time and money, it's not too difficult. You could also pay someone on Reddit to build this for you.
You will need a soldering iron, preferably with temperature control, solder, a fine soldering tip, a solder sucker, a sponge, decent eye sight and a well lit flat place to work.
Watch some videos on YouTube of soldering technique. Read some articles on adafruit. Watch a few videos of people building keyboards on YouTube. Wodan is pretty good, and shows the basic process. If it looks like fun, then go for it.
generalzouIt is actually pretty easy! I just completed the kit and now i type my first words with this thing, and i only did a little soldering project before this. I would recommend practising by desoldering and resoldering some stuff, like on an old dead keyboard or other electronic waste.
Just keep in mind a soldering iron is NOT a brush ;)
generalzouHonestly this is the best advice I read anywhere! Soldering is not rocket science... there are so many guides out there.. that want to make it rocket science. Just some simple tips take your time.