Regularly end up on roof to get bird (8)
I believe the answer is:
nuthatch
'bird' is the definition.
(nuthatch is a kind of bird)
'regularly end up on roof' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'roof' becomes 'thatch' (thatching is a kind of roofing).
'end'+'up'='endup'
The alternate letters of 'endup' are 'nu'.
'nu'+'thatch'='NUTHATCH'
'to get' is the link.
(Other definitions for nuthatch that I've seen before include "Trunk-climbing bird" , "Bird - hunt chat (anag)" , "Singer" , "Tree-climbing songbird" , "Climbing songbird" .)