If you have an LDD (Lego Digital Designer) file, usually extension .LXF, you can use that file to order the needed parts. I will guide you how to use my favourite page BrickOwl.
BrickGuider is a page where me and my son showcase our LEGO builds. We also collects other persons high quality lego build instructions & guides made by fans of lego. Everything you see on the site can be built by you!