Create a WordPress Multisite Plugin

I have a multisite installation. Now, I need to create a plugin that save every post of child sites on main site. For example: The main site is: [login to view URL] One child can be: [login to view URL] An user is writing a new post (is a CPT) that have some META-VALUES and TERMS (taxonomy), when this user to click on SAVE or PUBLISH, the post will be saved and published on [login to view URL] AND will be saved too on main site ([login to view URL]). When this post is updated by the your original owner, will be too necessary do the update of the post on main site. For some reasons, I cant just read the post for another blog, I really need to create the posts on the main site.