Sergio,
Though Steve and I are detailing this model with actual kitbashed parts, the model in itself can hold it's own in my opinion if you're not that picky. I feel that if you were to tackle building one from scratch it would cost more and take up a lot more time, and for me time is money. You have to make that determination for yourself.
There's really only two options at this point if you want a Studio Scale AT-AT. You can make one from scratch, or you can get this kit and detail it as Steve and others are doing. If you can afford it, I say get it! It'll save you a lot of time and materials from scratching it.
If anyone likes what I've done so far on mine, give a hollar on here and I'll explain what I did. I'm sure Steve will chime in also with any tips.
Rolando