How can you build faster within the first 5 minutes...? Or a better question is, what to build in the first 5 minutes....
I take it that you're new to the game =P? I think by playing through the campaign you should get a rough idea of what to build in the first 5 minutes. Also, how fast you can build depends on how much you practice.
if you want to build faster in the beginning, learn a build and practice it over and over again. Once you are in a real game and know your build you will be able to make changes to it on the fly based on what your opponent does. For more general advice, always build probes, and never store up minerals, spend it all ITS A BUYERS MARKET BUY BUY BUY!!!