My question Is are you asking for a tower for a 38mm minimum dia. rocket and how long is it and how large of motors will be used?
I have made up a adjustable 3 or 4 tube tower that uses 4' long tubes.
I used 1/2" EMT tubing and 10" pipe rings for it.
just a couple of pics of it. I have more and if this is what you are looking for I can let you know how it is made.
Just let me know.