1. A system for building a virtual appliance image using a pre-stored operating system image, the system comprising: one or more physical processors programmed with one or more computer program instructions which, when executed, cause the one or more physical processors to: receive a request to build a virtual appliance that includes an operating system, wherein the build request includes an image description associated with the virtual appliance; create, based on the image description, a root file system having a root directory structure that defines a layout of directories in which files of the virtual appliance are to be stored; identify, based on the image description, a pre-stored image for the virtual appliance, wherein the pre-stored image includes files sufficient to build an operating system, wherein pre-stored images, including the pre-stored image, are stored in a database, and wherein individual ones of the pre-stored images are derived from other ones of the pre-stored images; add the files of the pre-stored image to the root directory structure to augment the root file system; identify, based on the image description, one or more additional files that are not included in the pre-stored image to be added to the root directory structure; add the one or more additional files to the root directory structure to further augment the root file system; identify first and second sets of the pre-stored images such that first images of the first set of pre-stored images are images from which second images of the second set of pre-stored images are derived; analyze differences between the first images and the second images to determine statistics regarding types of changes made to build the second images; provide, to a user, one or more suggested changes to the augmented root file system based on the statistics regarding the types of changes; and build an image of the virtual appliance based on the augmented root file system.