Wire netting (and sometimes plastic netting) is used over thatch.
The reason for this is to deter birds from pulling at the straw in an attempt to get at any corn left after it was thrashed out.
Often a Water Reed roof will just have the straw ridge wired in.
Wire is occasionally used to add stability to a section of the roof: e.g. where the wind is high.
A cement flashing is applied as waterproofing around a chimney as a seal/join between the thatch and the chimney.
Cement can be used instead of lead and is usually applied by your thatcher on completion of a ridge which abuts a chimney.
This is a term used for a section of a roof that is extended to cover a lean-to or side room, so that it sweeps down from the ridge nearly to the ground.
Catslides sections of a roof can be large and impressive and definitely add character to a cottage.