The OTA will be based around a 'coopered' hardboard (masonite) tube, 12 sided. I know that this is not going to be the best material but at <£6 for a sheet, it's going to be cheap. The idea came from Toshimi Taki's ply tube, with an added pinch of thrift.

Using the timber cutting service at B&Q, I have 12 full length strips, each 75mm wide. I will run one edge of each over the router table fitted with a 45 degree chamfer bit, using fence, featherboards and a second pair of hands to assist. Each internal angle must be 150 degrees - one surface cut to 45 degrees and butted together in a cradle or sorts will give me a 15 degree gap to fill. I've got a couple of tubes of Hard As Nails from the pound shop to put in the caulking gun and a sheet of scrap laminate from which to cut the knife-edge ribs/baffles. Masking tape on the outside and a wet finger to smooth/smoosh the bead should do the rest. Variations in the technique might include the use of PVA or epoxy to seal the edges first - I'm planning a couple of test joints but impatience may get the better of me.

Outside, I'll give it several coats of quick-drying exterior Dark Oak varnish and on the waffle side (poor-man's flock), I've got some matt black chalkboard paint that might do the trick once I've combined it again - it's not been opened in over 10 years. I might give the inside a coat of primer first to help seal it.

I'll re-enforce the ends, bolt holes, handle mounts, etc with ply, as necessary, either inside, outside, or both.

If I can get away with building the tube for under a tenner and it lasts two or three seasons, it will be a success of sorts. If it's a false economy, at least I tried not to spend too much.