The poles on all my tents are all softwood.
I usually start with a planed 40x40mm 2.4m piece of timber. Most ridge poles are under tension from the guy lines so that is usually sufficient but you could go up to 50x50mm if you think it is really needed.
If you get it from B&Q or somewhere like that you can select a piece yourself. I go for the tightest, straightest grained piece with as few knots as possible.
At B&Q these come with a small radius on the corners which might be OK for uprights but for ridge poles you generally want it more rounded.
I put the pole on a couple of trestles supported on blocks with a V cut into the top which leaves the corner sticking upwards. I then plane the corners down to make an octagonal profile. I'm told this could also be achieved with a table saw but I don't have one of those so I can't tell you more about that.
Just to finish off a little more I usually run a hand Surform down the remaining edges which rounds the pole a bit more.
For the finial spikes I usually use brass rod because I don't have to worry about corrosion but any metal rod should do the job. Drill a 2-3" hole in the pole half a millimetre too small for the bar and then just gently tap it in with a hammer. I use 8-10mm for principle poles, 6mm for secondary ones. ( Secondary poles are ones that do not support ridge poles they just spread canvas. )
Drill holes with 1-2mm extra clearance in the ridge poles that the spikes have to go through to allow for movement and shrinkage. These holes are the weakest point so I usually whip the pole ends with some strong cord to strengthen them.
An alternative that I have used on one tent before is to use a long, large vine eye, with an internal diameter big enough for the finial spike, and screw this into the ends of the poles with a hole drilled as described above.
The poles on the left of the picture, made like this, have been used for about twenty years on one of my re-enactment tents, even withstanding gale conditions at Whitby Abbey one year. The poles on the right are new but I have used this method before with good success.
The middle two poles have been dyed and waxed to darken the wood. These are in public view and I prefer them to not look like DIY store timber. The ridge poles are left undyed as they are in contact with the canvas and it is never a sure thing how dyes, waxes and waterproofing will work together so I keep things simple. They’re not normally visible anyway.
A question came up on the FaceBook Page about making wooden tent posts and I thought it might be useful to record my reply here for future reference.
Shown above from left to right here are an old ridge pole from one of my re-enactment tents Made from an old banister rail with long vine eyes for the support posts. An awning support pole from the same tent (Also used as a principle pole on my table awning.) A secondary support pole for the table awning and the ridge pole from the same awning.