How I make a dog cage out of this

How I would do it: Firstly I would remove the shelves on the left and use the wood to cover that side. Secondly I would remove and dismantle the drawers (and they might be sitting on a "Shelf" too and then use that wood to cover as much of the sides as I can. I don't think that will result in quite enough wood to cover all of the sides and then I would just buy regular pine to finish it off and make a door.

How big is the dog? If it is a small dog, you could leave a sleeping platform using the lower shelf on the left, and if there is a lower shelf under the lower drawer, you could turn that into a food and water station. Remove the drawers and any hardware affiliated with them. You could maybe leave in the top one or two drawers for puppy supplies if there is enough room for the dog to stand and move around easily. I would go with the suggestion above of getting pine wood to cover the back and sides where needed. You will need to do something about having good air flow through the structure. I would suggest not having solid wood all around it. Perhaps you could use a frame and put in some kind of wire fencing to allow circulation and for the dog to be able to see what is going on around him.

I would put some linoleum on the bottom so its waterproof and easily cleaned in addition to the above.

How big is the dog??

Do you want a cage for inside or a house for outside? An indoor cage needs to be open on all 4 sides. Like a kennel.

Remember this is wood, if this is to contain a dog in the house, like a kennel - the dog can chew wood.

I really like that piece!

Lisa S. is right dogs chew wood. Plus you can't clean wood well. Go to the Salvation Army and get a real dog house. This would make a great desk area for children.

If the dog fits within the shelf structure (on the left), I'd combine several ideas here... laminate for waterproofing... and add (cut to fit) wire shelving as a cage material.

Still, as Mogie says, Salvation army as a source may be faster, as cheap (or cheaper) and more suitable!