I used to run a D20 Star Wars campaign years ago, and I created some At-St walkers for it. I created an original piece and then made a mold of it and created a few pieces. I used my AT-AT model kit and the chicken walkers with paper miniatures and they worked well. This was before I got addicted to plastic Star Wars miniatures.
I didn't buy the At-At miniature, but I've been using this kit with the miniatures. Even if it's a bit small to be used with the miniatures, it looks ok if there's no other vehicles around, but even if there is it's still better than nothing.