Just like the question of whether you allow your pet to sleep in your bed or sit on your furniture, the question of how far you will go regarding pet specific furniture is a thorny one. Obviously most pets are going to have a little bed of their own, or a dog house if you live in an area where it makes sense, but what about in an apartment in the city?
One company, Architecture for Dogs, has quite a few suggestions on the subject of DIY pet furniture. (Warning: this site has a noisy intro, so you may want to turn down the volume on your speakers.) The site showcases furniture designers who have each created a special project for their beloved pets.
Some are practical. Yoshiharu Tsukamoto and Momoyo Kajiima, architects working in Toyko, designed this piece for their dachshund:
Because of their short legs, it's hard for dachshunds to meet their masters' eyes. Also because of their short legs, it's hard for them to get up on chairs. Is there no good way to get closer to the eyes? Stairs? With those too-long bodies, they may throw out their backs. How about something like a folded slope? This works. Let's make it long enough so a person can lie down too. Sunbathing with your dachshund on the veranda is good. The area under the slope is like a burrow for small animals. They can train there, digging down there to catch their prey. If you connect several, they can go anywhere, and form any shape. Multiple stacks in an atrium space make a ramp for the dogs to go upstairs.
Others are created for purely aesthetic reasons. Kengo Kuma explains:
Mount Pug is a mesh-shaped "mountain" assembly of thin and long 600mm (plywood) pieces as "branches." By combining the unevenness of each branch to form hexagons and triangles, the "branches" begin to support each other like the cells of living creatures. The "mountain" can be assembled without nails or a bond. Pugs are clever and mischievous. They make full use of the mesh as a nest and plaything. Toys and snacks can also be hung on the mesh.
See all the projects and get instructions on Architecture for Dogs. For the record, architect Sou Fujimoto built the dog house/storage unit shown above for his Boston Terrier, and so can you.
(Images: Architecture for Dogs)

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My dad made our cats a stool that slides under the window sill in our dining room. He made it all with scrap wood from his shop, stained it nicely, and covered the top of it with a carpet remnant. It sits under a window that the looks out at the bird feeder. The love it, it saves the backs of the chairs, and occasionally doubles as somewhat tall seating.
My dad made a set of stairs at the bottom of their bed so the oldest cat can get on the bed now that she has arthritis. Personally, I have intentions of a floor to ceiling full wall bookshelf system that my cats can use for perching when I get a new place. It'll be better looking and more useful than the current cat tree.
Sure. Pet-specific furniture lets the animals live better in the house environment, and reduces anxiety for the pets and owners. The cat stool mentioned above is a perfect, brilliant example.
I made a custom guinea pig cage out of those grid shelf squares and some luan plywood. It's huge and takes up most of the living room, but the little ones seem happy - though they don't know how good they have it!
Our five cats have all the furniture in the house . . . they don't really need their own stuff. On the other hand, we have a long carpeted bench by an 8 foot window for them to lounge on. They also have a round carpeted elevated cat stand and a taller carpeted square perch. They will lay on the bench when the sun is shining but seem to prefer being on our chairs, our table, our bed etc. As for building permanent pet furniture . . . I wouldn't because of the problems with eventual move. Why build something you will day have to deconstruct?
I had to build things for my pet (and buy some cool designer versions I found) because the stuff they sell at the pet store is always SO UGLY. I'm not putting a beige nylon carpet cat tree in the same room with my $5k dream sofa! Not happening.
I have some of that ugly cat furniture in my house. I just figure, it's their space too so we all have to compromise. That said, sometimes the kitties just like a good old fashioned cardboard box to play with. It's not cute, but watching them play bring a smile to my face every time!
Why not? We have a litter box trunk (to hide the litter box on the main floor) and cat flaps to litter box "closets" elsewhere. Shelf extension for the window sill for cat napping. Thinking of stair-stepped shelves on the wall for climbing...
But basically, no place (except the guest room -- some friends have allergies -- and the clothes closets) is off limits, so they have lots of furniture to climb and sleep on.
If my cat won't use those nice cardboard scratching pads instead of my carpet, what's the use of pet furniture? Methinks they designers are using hired models for their presentations. My $40 cat bed? "MEH!" says Zoey. She likes to sleep in a cardboard beer box with her towel and toys.
I tried to make a playhouse for my cats but they preferred their stupid cardboard tomato box. Yesterday, I finally took away the thing I made (that they wouldn't use) and am using it for shoe storage in my closet!
http://dodiegoldney.wordpress.com/2013/02/20/the-secret-is-to-know-when-to-stop/
Definitely! My husband and I hacked a piece of Ikea furniture for our rabbit hutch. Now that we have a few power tools we are building one out of real wood. Options for small animal cages are not pretty and I don't understand why. Cages should be practical and fit the pet's needs, but they certainly don't have to be ugly!
One of my first projects in my new apartment was to build a cat tree. My original cat was downsizing from living in a decent-sized house for 12 years, and I was adding another cat who is very energetic and needs to keep busy. So, of course, they have their own needs that should be considered when arranging a space or choosing furniture.
For the cat tree, I used part of a pallet for the base, then sandblasted some 3-6ft logs to use as the pillars, then made platforms out of the same pallet and covered them with fabric. I secured everything with a lot of screws, so it doesn't even wobble when they spring off of it.
It's not the most glorious thing I've ever laid eyes upon, but the cats love it, and It's just the right height for them to jump on top of the kitchen cupboards and hide out. The best part is that it cost me nothing besides the screws.
I just finished building a cage for our two new bunnies Fritz and Daisy. Once I get around to sewing some cushions for it, it's doubling as a window seat in our tiny, chair-sparse apartment. They, and their big brother Percy, have full run of the apartment, but they're getting better about using their cage for their necessaries.