Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
sŭper-strŭo, xi, ctum, 3, v. a., to build upon or over, to superstruct (postAug. and very rare): ligneam compagem, Tac. A. 4, 62: moles, Sen. Contr. 1 prooem. fin.: quidquid his (fundamentis) superstruxeris, corruet, Quint. 1, 4, 5: desuper pulvillis superstruunt, App. M. 10, p. 248, 27.