One avoiding heat rests - these may act as sunshades (8)

'sunshades' is the definition.
The answer and definition can be both man-made objects as well as being plural nouns.
Perhaps there's an association between them I don't understand?

'one avoiding heat rests these may act' is the wordplay.
I cannot really understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
'act' could be 'roll' (roll is a kind of act) and 'roll' is found in the answer.
The remaining letters 'bes' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).

'as' is the link.

Can you help me to learn more?