I realised that our corn snake was growing when she suddenly didn't fit in her favourite hide. She crawled in, curled up and it popped off her.

It's not just cornies; many species of snake like a snug corner to hide away in, especially when they are getting ready to shed their skins (see also my Shedding Box instructable). Their "perfect" space for most snakes is exactly the same size as they are, so as your snake grows you will either have to keep investing in larger and more expensive commercial hides, or just make your own. If you have a corn snake, a lack of a "just right" space can actually cause the animal stress.

This is how I upgraded Elsie's accommodation...

Step 1: What You Need

Firstly, please do not be discouraged by the fact that I use a laser-cutter in this project - the design is simple, and can easily be recreated with hand-tools.

Basically, you need some sheet material (I used 3mm ply wood), something to cut it, and something to glue it.

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Step 2: Design

Whether cutting by hand or by laser, my go-to resource for box-based projects is the Makercase website.

You enter the basic dimensions of your project, the thickness of your material and select your choice of joint style, and download an SVG file to edit.

You then use your favourite vector-editing software to turn your basic box into a hide;

Remove the bottom (you could leave the bottom in place, but if your snake defecates in there, you'll probably end up throwing it away).
Smooth off the bottom finger joints (if you are using Inkscape, you will need to use the drop-down Path menu to turn the pieces from objects to paths before you can edit the finger joints).
Add a door that is just the right size for your snake (I tried measuring Elsie, but she turned out to be too ticklish...)
Add any decoration you like.

I have added the SVG file I started with, and several versions of the files for the final hide, so you can recreate or edit it how you like (the files here don't include Elsie's name).

Step 3: Cutting

Simples - cut your material of choice in the manner of your choice.

If you cut by hand, make sure you finish off the edges properly - sharp splinters could harm your snake.

Step 4: Gluing

Again, another simple step - use whatever glue is appropriate for your material.

If you're using acrylic or other plastic, superglue is fine to use (I've checked with experts), just give the glue time to cure properly before you put it in the tank.

Other glues:

Hot glue may not be strong enough for large snakes.
Epoxy glues are probably fine, but check the pack for environmental information (if it says it may harm fish, it could harm snakes as well).
Solvent-based glues *may* be fine, but you need to check specific brands, and make sure all the fumes are properly vented before introducing it to the vivarium.

Step 5: Using the Hide

Snakes vary widely in intelligence, but even the dopiest animal will realise that there is something new in the area, and it doesn't smell quite the same as things did before, and may avoid the new hide for a while.

However, most will also work out fairly quickly that the new thing is (a) not dangerous and (b) quite comfy.

I put Elsie's new hide in place just before a family meal out. When we got back, she had abandoned her other "proper" hide that cost nearly £15 ($22) from a pet store, and was curled up fast asleep in £2 ($3) worth of plywood.