Tools & materials needed:
30 x 30 cm (11,5''x11,5'') Wood for base
Cardboard tube 60 cm (23,5'')
Wood to keep tube standing firmly
cca 25 meters (75 ft) of rope
Rope: cca 10$ (can be much less, depending on the type of the rope)
Wood material: 3$
Screws, drill, tape: found at home
Step 1: Make It Sticky
I used cardboard tube 8 cm in diameter (3,12'') and 60 cm (23,6'') long. First I have put two-sided tape around it as shown on photo (I didn't peel the protecting layer so the outer side of the tape doesn't stick to things around). You could actually stick the tape around the tube in a spiral way but i found this method to be easier.
Step 2: Cover the Tube With Rope
Peel one part of the tape at a time and tightly put rope on it in a spiral. I suggest using gloves at this step. Make it as firm and tight as possible and as the result the scratching post will be more durable.
Step 3: Making the Base
I had piece of wood about 80x30 centimeters (32''x12'') but I wanted a square base so I made two pieces of 30x30 cm. Then I put one above the other and connected them with screws in order to make it more stable but I don't think it actually makes any difference because the base area is more important than weight.
Then i had to make some kind of "tower" that will be firmly connected with the base and which will go inside the tube in order to make it standing upright. I made it by doing a cross with wooden pieces about 20 cm long. Ideally it should be long as the tube itself but i only had this much of a wood so... I really didn't put much effort into this part (no sanding, splinted wood...) This part has to be as wide as the diameter of the tube is (in my case 8 cm). I put some glue on the connection of the parts just in case.
Step 4: Covering the Base With Fabric
I bought some fabric that seemed not so smooth so the cats could scratch even on that. They don't. But still, it looks much more professional :)
I made a stripe of 60x30 cm (i.e. two parts of 30x30 cm) + about 2 cm margin on each side to make nicer, folded ends. On one part of the fabric I cut a cross in the middle. Through that cross will be going that central part that holds the tube. You could make a circle but this is simpler and it really doesn't matter because it won't be seen when completed.
First I put hole over wooden central piece and fixed fabric to the side parts of the base with nails. Then I folded the other half of the fabric and covered lower part of the base and finally fixed everything with nails again.
Here's a scheme of fabric with marked place to cut hole/cross. Grey outer line is margin
Step 5: Putting the Tube Onto the Base
Finally, the last part is to get two final pieces together. Simply put the tube onto the tower on the base and push until it is settled completely. It shouldn't be too difficult or too easy but just with enough force. If it's too loosely it might not be stable enough and the cats might not like it.
Suggestions! Don't use empty tube as I did. Simply use round piece of wood about 10 cm in diameter, put the rope on it in the same way and connect the wooden piece with the base. That way you will save yourself of doing that central cross-shaped piece.