So I’m writing away (or trying to) in my alternative version of 11th century Ireland., when my characters had to thatch a shelter. Yikes, so how does one thatch a roof?
A common reed (phragmites communes) is one typical plant used for thatching. Also wheat straw is used but care must be taken not to damage the straw during threshing (removing the grain from the stalk).
And when you get done, you can trim the roof: