Outdoor shelter rebuilt there to overlook river (4,5)
I believe the answer is:
tree house
'outdoor shelter' is the definition.
(shelter attached to a tree)
'rebuilt there to overlook river' is the wordplay.
'rebuilt' indicates anagramming the letters.
'to overlook' says to put letters next to each other (in a down clue, some letters go above others).
'river' becomes 'Ouse' (Yorkshire river).
'there' is an anagram of 'treeh'.
'treeh'+'ouse'='TREE-HOUSE'
(Other definitions for tree house that I've seen before include "Children's play space in the branches" , "Two kinds of box" , "Building in the branches" , "in which children play" .)