There is very little information on the breeding biology of the Rufous Wren (Cinnycerthia unirufa) and, more specifically, there appears to be no published information regarding its nest (Kroodsma & Brewer 2005). On 13 November 2014, I filmed two adults building a nest at Tapichalaca Reserve, Zamora-Chinchipe Province, southeastern Ecuador. The nest, an oval structure of dry grass, moss and twigs, was 5 m up in a tree. It measured about 15 cm across and had a lateral hole some 3·5 cm wide.
References
Kroodsma, D. & Brewer, D. (2005). Rufous Wren (Cinnycerthia unirufa). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.) (2014). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona.