I made it a little deeper to accomodate my tuner (59" wide x 21" deep x 35" tall).
I liked the look of the long, top shelf that others makers had built, it's perfect for my 3 front speakers!
These sliding door rollers worked great for the door hardware:
I used 1" x 0.125" flat bar (hot rolled steel) for the rails and door mounting stips (6" x 4). It's fairly soft, so is easy to drill the holes for the screws.
Total cost was about $250, but $80 of that was for the thick cedar top. I used cedar, as I like the colour it goes when ebonized with vinegar/steel wool solution. The door are also cedar. I finished the top and doors with wipe-on polyurethane. The paint was grey eggshell latex.