http://beheco.oxfordjournals.org/content/12/4/390.full...Although females appear to prefer mates that build nests with certain characteristics in some species (e.g., Collias and Victoria, 1978; Hoi et al., 1994; Sikkel, 1995), it is unclear whether this preference stems from a choice for the nest per se, or for some correlated quality of the builder. Male bowerbirds construct elaborately decorated bowers (which are not nests, but courtship arenas) and females prefer builders of higher quality bowers as mates (Borgia, 1985b). Males that are able to maintain high quality bowers are also those most able to withstand raids from other males (Borgia, 1985a), suggesting that they are dominant individuals and that females use the bower as a “marker†of male quality (Borgia et al., 1985). If nest structure reveals traits of the builder that may be correlated with either his paternal ability or his genetic quality, in the same way as do bowers, then nest-inspecting females could use this information in mate choice decisions...
It's rather complicated, but this article suggests it does come down to utility.
