“Slide shelf”(?) for Mitre saw

Depending on how precise you need to be, I think a slide out shelf for it might be a mistake. If your miter saw is anything like mine, it's not light, so it's going to be tough to come up with a solution that doesn't sag when you extend it out. Add the weight of whatever material you're cutting, and it's going to get difficult to keep it flush against the fence and get square cuts (unless you make your slide out shelf out of glued up 2x4s or a box or something). I just finished building my miter station a few weeks ago, and I just put the whole thing on casters. Not sure what your tolerance would be for that, but if it were me, I'd rather do that and keep the saw stable. Just roll it out a bit when you need to use it, and then tuck back against the wall when you're done.