I turn all the finials by hand myself from stock timber. Did you know they are not just for decoration - they actually perform a really important function....
In high wind conditions/storms a blanket of wind will pass over the top of a building and cause negative air pressure below it – this pulls material out of roofs, and can lift sheds and greenhouses clear off their base. This is very unlikely to happen given the substantial base these greenhouses have. However, it is an extra worthwhile precaution. The finial works by breaking up that blanket of wind and prevent the wind uplift occurring.
You will see the similar function is provided by the small point of metal at the end of aircraft wings – preventing drag - a blanket of wind pulling the wing back. The finial needs to be high enough to stick a finger up into that wind blanket and break it apart.
Click on each