thats a good general guide on how to make yourself a cage/enclosure. if you want to have a side that covers it all instead of having an open box like this guy made, you can easily rivet a couple hinges onto one side of it with your lid, or just bend down one more side so that you have two stubby faces like the one he has at the bottom of the opening in the last pic. your lid would be just a single sheet with no folds. to fasten it in a way that you can easily remove, you can use riv-nuts, which is similar to a rivet, except when you compress it, there's no "nail" to break off, and it leaves a threaded insert behind. quite handy if you have the room inside your enclosure to actually have a nut and clearance for a screw/bolt to go thru it without hitting whatever's inside.