I've made tons of cages, stands and racks over the years. I've have no 'training' or 'professional experience' with woodworking but I do find it fun to build things...
This is my most recent one, an 8' x 3' @ 3.5' tall enclosure for my 4' Tegu that doubles as a stand for a fish tank. The tank in place is a 125 gal but the stand will accomodate up to an 8' x 2x @ 25" tall 265 gal aquarium.
It's made much bulkier than a typical enclosure needs to be as it's built to hold in excess of a ton of water on it. For a simple lizard (or snake) enclosure a simple 2"x2" lumber frame shelled with 3/8" plywood would be sufficient (and A LOT easier to move).
The frame and shell are the important parts and the easy parts. It's the finishing stages that require more 'skilled' work. If you are happy with a painted finish, painting is simple. If you want to stain it, stain work is a bit more complicated but still not too bad. The biggest lesson I learned with staining is that extensive sanding is critical.
For me, the door was the most complicated part. I went with swinging doors as I like to be able to open the whole thing up and have access to the entire enclosure. But sliding doors are much easier to construct and install.
Standard glass is fairly cheap but comes with some risks. Plexiglas is more expensive than standard glass and comes without hazardous risks, but scratches very easily and once scratched is nearly inmpossible to buff out. I used tempered glass which cost the same as Plexiglas, if very difficult to break and has the scratch resistence of standard glass. I simply looked up glass shops in the Yellow Pages and called around comparing prices until I found one that made me happy.
Having the right tools for the right job is a very important detail. As mentioned measure twice (or more) and cut once. Plan plan plan plan plan! Study your drawings well and know them thoroughly, but still refer to them during ever step of construction. make sure your 90 degree corners are 90 degrees. If you have any hesitation to do something better, hesitate and do it better. If you get frustrated with a step, take a break.
Most importantly, take yoru time. Gettign the enclosure done quickly usually results in havign to make another one sooner. Take your time, think it through and do it right. That way you will have an end product that you and your animal can enjoy for many years to come.
Oh, also research the products you wish to use. I have foudn Drylok to be a very impressive product for sealing anything animal related.