What material best for a custom amp stand

I plan on having a custom amp stand built to hold my current 250lb 2 channel amp. I will place it behind closed doors so appearance is not important. I was planning on having a metal shop create something (although I am open to other ideas). My only requirements are that it support the weight, that the platform is approximately 6 inches off of the ground, and that it doesnt vibrate. It will rest on a concrete floor. Thanks in advance for your input.