In my case I used 2 lengths of 1 1/4" and 1 length of 1 1/2" The 1 1/4" fits inside the 1 1/2 ". I used a 1 1/4" for the bottom the 1 1/2" for the center and the final 1 1/4" for the top. Over lapped them maybe 2 feet then through bolted them together with 2 bolts for each joint. Ended up with a 26 foot mast. Putting the larger piece in the center position made the whole thing stiffer.
It is mounted with the bottom sitting on a block with a clamp on a second floor deck. It extends up to the peak of the roof where it is attached to the end of the ridge beam. It sticks up about 7 feet above the roof and has 2 antennas on it. A copper tube Slim Jim from KB9BVR Antennas. It's the Land Mobile version for MURS, VHF, Marine VHF and my scanner. Below that about 2 feet is an Arrow Antennas 7 element GMRS Yagi directional. If I want to rotate the Yagi I just walk out the door of my radio room and twist it. But I don't need to do that very often.
That's how I did mine but everyone's situation is different so you just need to be creative.