Roundwood vs Square wood Roof Poles

[Yurts_latvia]

Hello again,

I hope this question hasn't been covered too much before and therefore can help others too...

I'm just making my second 14 foot yurt with roundwood aspen poles, they're about 30mm in average thickness.

I went for roundwood partly because it seemed a lot easier to drill round mortises into the crown. But I've noticed how they twist in the holes, possibly making the crown less-secure, and wonder if square wood and mortises would make everything a bit tighter.

+ I'm curious to forge the tool to burn square mortises into the crown. What would be the correct name for that?

What are the pros and cons of using roundwood vs square wood for rafters?

I've noticed square or rectangular rafters are often elaborately shaped into an octagonal profile which, whilst attractive, must require a lot of work.

My friend tried using rectangular wood and kept the pieces square, it seemed to work ok for her. Is this ok practice too?

I was thinking instead of 30mm roundwood, I could use 18mm x 45mm milled softwood, for a light-duty 14 foot yurt. And thicker pieces for a year-round yurt. Does this sound about right?

Big thanks to anyone who can point me in the right direction with this one!

Charlie