It's easy to think that you should use the thickest materials you can, but the effort required to panel-mount most things in, say, 2" wood is... non-trivial. It can be done, but it's kind of a pain. Also remember that unless your (school?) shop has the correct tools, making non-round holes - IEC jacks come immediately to mind - can be a double-plus unfun challenge, especially in thicker metal.
Head-Fi users seem to obsess over heavy, overbuilt aluminum enclosures, but don't be afraid to use whatever materials you prefer. I tend to prefer a simple kind of retro late-1950s look - light or moderately light wood, like cherry with a tung oil finish, with aluminum or acrylic front panels and large, low-profile knobs - but that's very much not everyone's cup of tea.
Oh, yeah, important final piece of advise: Never build a project enclosure you can't reasonably easily reopen later. There's nothing quite like saying "you know, in retrospect, maybe wood glue wasn't such a good idea"...