Songbird principally nesting under material on roof (8)
I believe the answer is:
nuthatch
'songbird' is the definition.
(nuthatch is a type of songbird)
'principally nesting under material on roof' is the wordplay.
'principally' indicates taking the first letters.
'material on roof' becomes 'thatch' (I can't explain this - if you can you should give a lot more credence to this answer).
The first letters of 'nesting under' is 'nu'.
'nu'+'thatch'='NUTHATCH'
Can you help me to learn more?
(Other definitions for nuthatch that I've seen before include "Songbird named from its penchant for a kind of fruit" , "Songbird feeding on insects and kernels" , "Singer" , "Tree-climbing bird" , "[FEATHERED FRIEND]" .)