What material do you plan to use? I made one out of melamine, it ran about $200 or so to build. Plywood would be close in price, with a few options on connecting together. The trickiest, yet cheapest would be imitation hardwood flooring, also need a table saw to cut grooves in 1" x 2" pine corner supports.
If you aren't handly with tools , not all of us are .
You can use 1" SQR hollow aluminium tubing and CONNECTIT nylon connectors to join the precut aluminium tubing together very nicely to form a nice strong yet light box frame.
All you need is rubber mallot to knock the tubes into the joiners.
Any hardware store who sells plywood or even internal timber wall panels will cut a sheet or two to your exact specifications , ie
3 sheets 4ft x 2ft
2 sheets 2ft x 2ft
Then all you need is a power drill and drill driver bits and a bunch of self drilling self tapping screws to attach the wood sheets to the metal frame. (No glue needed.)
add some hinges or plastic sliding door tracks and either a couple of 2ft x 2ft x 6mm thick acrylic sheets (for doors) or a get a glasier to cut some laminated glass to make two sliding glass doors to fit.
Vents : round plastic cupboard vents work well , are a breeze to install, all you need a suitable size hole saw and they slide in very snugly.