If you make it out of "solid" wood, turned on a lathe or not, to get good dimensional stability it will have to be glued together from many thin (say, 2cm x 2cm and surely not bigger than 2cm x 5cm) strips parallel to the axis of the tube, with alternating grain directions. The project is quite an excercise in wood jointery.
If you just glue up 6 or 8 pieces and turn it on your lathe, it will probably warp like crazy. If you want it to look like it was carved out of one solid piece of wood, you will probably have to resort to a veneer.
I think a 6" f/8 is small and forgiving enough to use a wooden tube. A 6" f/8 is pretty much forgiving enough to use just about any reasonable kind of construction technique or design and still be useable.
I would put the optics in a cardboard tube and use the telescope while I was building the wooden tube... Combine instant gratification with long term goals.
Chuck