Blender

So, I've done some tutorials in Blender, and I want to start modeling. Problem is, I don't know how big to make things. Will someone who uses Blender make a .blend file with maybe just a cylinder as high as a person should be? It would really help. Thanks in advance!
Edit: Now that I've googled it, I can't find the Mac Blender .dts exporter, so if someone knows where it is, a link please?