Finch cages are special, and more difficult to find, because they need to be longer than they are tall. Finches fly horizontally rather than climbing like the hookbills. Most commercially-built small bird cages are at least twice as tall as they are wide, the wrong type for finches.
One advantage of owning finches is that they do not destroy their surroundings by chewing, like with the hookbills, so you can build their enclosures out of wood without worry.
What dimensions you build your cage are up to you, depending on the number of birds to be housed and where you want to put the cage. I built mine 48" long, 18" wide and 18" tall, and it fits nicely on a low coffee table under a window in my bedroom.
You will need the following supplies:
½" plyboard
1" x 2" lumber
1" x 4" lumber
½" wire mesh (smaller for very small waxbills, if desired)
1/8" plexiglass
hardware such as screws and nails
carpenter staples (if you have a staple gun, this will come in extremely handy!)
clear, sticky-sided contact paper (sold in rolls to line cabinets and drawers with)
small metal clips and/or magnetic tape
paint
small, flexible wire or small plastic zip-ties
1. Out of plyboard, cut the floor of your cage (I used 18" by 42") and two short sides (I used 18" by 18").
2. If you wish, cut "window boxes" into the ends to form doors or windows, but make sure there is at least 3" of plyboard on each side for support.
3. Affix the ends perpendicularly to the outer edge of the floor piece.
4. Cut two equal pieces of 1" x 2" lumber the exact length of the floor piece.
5. Affix a 1"x2" piece on each upper corner of the end pieces to form the box.
6. Cut two equal pieces of 1" by 4" lumber the exact length of the floor piece.
7. Take one 1"x4" piece and affix it flush with the floor and both ends. This will be the BACK of the cage.
8. Affix the other 1"x4" flush with the ends on the FRONT of the cage, but leave ½" to ¾" of space between the bottom edge of the 1"x4" and the floor piece. This will allow you to slide the cage tray (plexiglass) in and out of the cage.
9. Now you are done with the frame of the cage. At this point you should paint the cage.
10. After the paint has dried completely, line the interior surfaces of the cage with the clear contact paper. This will prevent corrosion of the paint or wood (the liner is waterproof) and allows for very easy cleaning. It can also be easily replaced if it starts to peel (although, after two years of use, I have not had to do this with my cage).
11. At this point you will need to install the wire mesh. The wire mesh must be affixed so all ends of the wire are on the outside of the cage, to avoid injuries to the birds. Stretch 3 pieces over the two long sides and the top, and use the staples to secure the wire into the plyboard ends and the lumber side curbs and roof supports. Good quality wire mesh should not sag or distort with age. Be careful when stapling the wire to the 1"x2" boards as these are more fragile…they need some support. Also remember to cover any "windows" on the short ends with mesh, or install wire doors over the holes. You can make a swinging door by cutting a piece of wire mesh, with at least 1" of overlap, and loosely securing it with staples on the top. You want the door to swing open from the bottom, because a door with the hinge on the side can accidentally be left open, but a door with the hinge on the top will always swing closed. For the side door on my cage, I attached a strip of 1" by 2" lumber on the bottom edge to weigh it down, and to that and the part of the cage side it touched I put magnetic tape. You could also use metal fasteners of your choice. Luckily finches aren't too pushy so they are unlikely to escape with even minimal strength of the door latch.
12. Cut holes in the wire mesh for doors on the front and top of the cage and form the hinges from small, flexible wire or plastic zip-ties. Again, the hinges should be on the top edge of the door. You can use metal snap clips to fasten the doors closed on the bottom, or metal binder clips (that's what I use, they work fine and are easily replaced!). Remember, allow at least 1" of overlap for the wire mesh over the door opening, to prevent escape of your birds.
13. Measure and cut the plexiglass to cover the bottom of the cage. It should slide easily in and out of the slot in the front of the cage. Plexiglass is easily cleaned and replaced if cracked or broken. When cleaning my bird cage, I clean the plexiglass with glass cleaner, cover it with layers of newspaper, the slide it into the cage. To clean the bottom of the cage when the plexiglass is removed, I use a drafting brush (you can find it at an art supply store…it works perfectly to sweep up seed hulls) and glass cleaner if needed.
Now you are done with the cage and ready to "decorate!" Natural branches and twigs are best for perches and can be configured in any manner within the cage. By placing more perches at the ends of the cage and few in the middle, you will encourage your finches to fly back and forth and they will be in better shape. Under the same premise, place food and water containers on the end opposite their nest. I use small plastic plant dishes (the kind that go under a potted plant to collect runoff water) for their seed and water. These are inexpensive, dishwasher safe and provide enough space for the birds to bathe in the water. Watching the birds take a splash is the cutest thing.
Best of luck with your cage building and please let me know how it turns out.