Storage space costing this oddly: a hundred (5)
I believe the answer is:
attic
'storage space' is the definition.
(an attic may be used as storage space)
'costing this oddly a hundred' is the wordplay.
'costing' becomes 'at' (as in a shop stocking items 'at' a certain price).
'oddly' means one should take alternating letters (letters in the odd-numbered positions are used).
'a hundred' becomes 'C' (Roman numeral).
The alternating letters of 'this' are 'ti'.
'at'+'ti'+'c'='ATTIC'
(Other definitions for attic that I've seen before include "Lofty room" , "Top chamber" , "Top apartment" , "Upper chamber" , "Of Athens" .)