My first kit was a Zen. It is difficult for a first timer, but very doable. There is only a schematic and a few low-res pics to look at. I've since built four kits, and every time I get better at it. The thing is, it's fun to build but after you're done all that matters is how it performs. I've had a few problems with mine along the way, and it's been a pain to rectify the mistakes I'd made. Also, in the back of your mind you might wonder how yours compares to a Zen built by Decware sonically, that is until your comfortable with your skill. OTOH, it's been a wonderful learning experience that I wouldn't take back. Through experience, I've built up enough courage to try many of the expensive boutique parts that can really set a kit apart from the production Zens. And, in the long run my enjoyment of music has benefited even though my wallet hasn't. Point is, don't do it to save money. Do it for the experience and learning.
And if you have any questions along the way, there are many here who can help

-Brett