I want to build a fly tying workbench. I want it to go on top of a desk.

Size is not a problem, big enough to be of use but no so big to be unwieldy. I would like it to be semi-permenant, but so between seasons or if I need to I can stack it away.

I want everything at hand. I have good woodworking skills so don't want to buy one, and I wondered if anyone here had built their own they could give me some ideas for the ideal. Also if they can supply some dimensions etc....