Asked
— Edited

Ok. So. I started to make my trek towards a 3D printer today by attempting to make a simple notepad holder in 123D design. I followed the technique that Ben used in this video and I discovered something different.
When I try to extrude the outer walls of the shape it simply makes one big box that swallows the bottom of the box. I can post my project file if nessesary. Will post video with problem.
Also, last I checked the online version of 123d was better than the downloadable one, there are more tools available.
For further guidance, my ARC reactor was drawn up in 123D, the methods I used were...
Each section was drawn individually, i.e. the base of it (the thick part with the fins), the centre part (circle with 3mm holes for LEDs and 3 spokes to attach to the base) and the top part of it (the rings with the blocks with the copper wire around them). I tackled each part on it's own, grouped it then moved on to the next and put all parts together as one.
Most of it I start off with flat shapes such as circles and squares, draw it out, delete the cut out parts and then pull it up to make it a 3d solid. For other cut outs (like the 3mm holes for LEDs) I draw flat circles on top of the 3d parts and pull them down through the solid.
This is what works best for me, see how if works for you. Like I said, we all do things differently and there isn't really a correct way, there are several correct ways.
Hope that's of some help to you.
I figured it would be the other way around too but for a change I guess AutoDesk wanted to mix it up a little