Cwm Eigiau is a harsh place to live in, it's a wide valley and very long as Rhuddlan and myself can testify when we walked down the valley some time ago.!
I don't blame William Bartleet if he didn't live there but he had three shepherds and they may have lived in a Hafodty to protect and look after the sheep. A Hafodty or Summer House is where they would have stayed in the Summer months but in the Winter they brought the sheep down to lower land for shelter from the harsh and severe Winters on those uplands.
There must be some records from the farm, tax or tithe and they may be in the Conwy Archives but I've never looked for any before. I'll make enquiries when I go there next time.