>>To be honest I am concerned with the animals happiness and comfort for the best price that I can get. The weight is not a concern and I am not worried about it being attractive.
That sounds like an admirable goal.
I would say to use melamine coated particle board. It will require no finishing on the interior or exterior which saves money and time. And it's more than durable enough for bearded dragons.
>>I was thinking of making the cage 60 x 24 x 24.
I think this is a nice size. It allows versatility for lighting heating and will be large enough for a trio of adults.
You may waste some material, however, since most sheet goods come in 4'x8' sheets. A cabinet shop may have 5'x10' sheets, however, or be able to cut some of your panels from scrap. The melamine they carry tends to be of higher quality (more durable, better particle board) which is also nice.
Another choice is to build the cage from melamine shelving available from Home Depot, etc.
A friend of mine asked for a 6'x2'x2' cage a few years back and I ended up using 6' melamine shelves from Lowes or Home Depot. They offered a few advantages.
1) Three of the four cut edges already had edge banding applied. You can't beat the quality of the edge banding on these prefabricated shelves. For one, they start with the higher quality melamine, then they professionally joint the edges, and then use a machine to apply the edge banding that cost more than my house. Ends up being a much better job than I can do with a circular saw and my wife's iron.
2) It was the higher quality melamine (as mentioned above).
3) It was already cut, more or less.
4) With no waste it ended up costing the same as if I had cut the panels from 4'x8' sheets.
I just bought three 6'x2' shelves. One of those had strips cut off or it to make the face frame. That was the back panel, making the cage only 18" tall.
The other two shelves made up the top and bottom. An additional 4' shelf was cut in half to form the sides.
That's another thing to consider - a 6' long cage may be as inexpensive to build as a 5' cage.
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Current snakes:
1.1 Gonyosoma oxycephala - (Silver/Yellow)
2.2 Gonyosoma oxycephala - (Green)
4.3 Gonyosoma janseni - (Black)