Heres how to add build to the context menu of a sln file..
note: you only need the tool for vista.. xp and 7 let you change and add context menu operations in the folder options->file type menu..
so, if you are on vista, download from http://www.creativelement.com/powertools/#download
when you start it for first time, check the "Edit File Type Associations" box, theres loads of other good stuff but ill let you discover
now right click the sln file and select edit file type
type Build (debug) for the top text box
then paste this in second box (which application to use)
and this in the final box (command line op)
/k C:\WINDOWS\Microsoft.NET\Framework\v3.5\MSBuild.exe "%1" /p:Configuration=Debug /t:Rebuild
Now go back to the sln file and youll be able to right click and build..