With all the snow we're having I thought it was appropriate to post a link, http://www.wikihow.com/Build-a-Snow-Fort on How to Build a Snow Fort! On the website, Wikihow to do anything, there are detailed step-by-step instructions for constructing a fort and decorating it with dye. In addition there are safety tips such as never entering the fort alone, a list of necessary gear for building and an awesome (although long) video of actual building of a 3 story snow fort.
If by some chance you're not physically ambitious then you may want to look in this book for other building ideas. Steven Caney's Ultimate Building Book is one of our library's heaviest books and filled on each page with everything you'd want to know about different types of structures and how they are built. Photos and illustrations and many projects are included that will satisfy the enthusiastic builder in you!!
My students call me "Lori the Librarian." For the past 25 years I have had the best job as School Librarian in the Aaron Kushner Library for grades K-3 at the Solomon Schechter Day School of Greater Boston.