Step 1: Imagine all the people, wait, I meant dimensions
It's important to have the dimensions of the wand or object in question in mind.
My wand has a maximum diameter of a bit more than 2cm and a length of just about 36cm. With foam padding a box of about 4x4x40cm would do, but I want a slightly bigger one as I might add some additional stuff. Or not, I don't really know yet, but I'll account for it anyway.
So what I want is a box about 8cm wide, 6cm high and 40cm long. This addidional width, length and height will also account for dimension loss caused by several layers worth of cardboard as well as leave enough room for fitted foam padding.
So let's calculate just how large that posterboard strip we need is going to be:
Intended width + 4x intended height = Width of the posterboard strip (8 + 4*6 = 32cm)
Indented length + 4x intended height = Length of the posterboard strip (40 + 4*6 = 64cm)
Cut a posterboard strip of the correct dimensions (32x64cm) using a sharp cutter knife.
Due to my flap design some flaps (especially the outer flaps) might end up being a tad too short to cover the box all the way down to the bottom. For a fitted box filled with foam pads this is irrelevant, but if you want to make a simple box without filling, add a safety margin of about 5 milimeters to all directions / any of the outer flaps just in case.
Step 2: Sketch the box (picture #1)
Now that we have our strip we can mark down where cuts and where fold lines will be.
I marked every crease with a dashed line and every cut with a full line using a silver metallic gel pen just so you will see it better in the pictures.
You can go with different flap designs and dimensions, but this will result in a really nice-looking box.
Step 3: Cut It, Crease It, Fold It, stretch It (picture #2)
I cut every line that needed to be cut using a cutter knife. Be sure to use a sharp blade and a metal ruler with a cutting edge for clean cuts.
The reason I made the side flaps of the long outer flaps 6x4cm instead of 6x6cm is that the box bottom is only 8cm wide and I did not want those flaps to overlap, adding unnecessary thickness to the side ends of the box.
As I recently started to invest in some leatherworking tools I have the pleasure of using a bone creasing tool to mark the creases of the box before folding it. It is an incredibly useful tool and quite affordable to boot. Just run it along every crease line once or twice with a bit of pressure and the folding gets so much cleaner and easier! Alternatively you could use an empty ballpoint pen or pretty much anything with a rounded, non-sharp point/edge.
Next I folded every single piece a full 180 degrees in one and then the other direction to work the fold a bit for easier glueing later on.
Step 4: Glue it together (pictures #3 - #7)
I started with one side of the box by attaching the 6x6cm flaps of the short inner flap to the long inner flap. Just so that I don't have to wait ages I used crazy glue for these, but rubber cement for the rest.
The glued pieces were held together and put under pressure for about a minute so I was sure they would stick. It helps to put the surface currently being glued on a flat surface (basically, press down against your table).
The process was repeated for the other flap on the same side of the box so you ended up with picture #3.
Pictures #4 + #5:
Now that the long inner flap has been secured, the long outer flap including attached mini-flaps can be glued.
I put on glue as seen in picture #4, then folded the long flap over while keeping the small flaps out of the way and pressed the long flap down first. It helps to run a metal ruler or your fingernail along the crease line to prevent it from popping back up. Long flap firmly pressed down I moved on to the attached short flaps and pressed them down as well. The result can be seen in picture #5.
The process from the pictures #3 - #5 has been repeated on the other long side so that I ended up with picture #6.
This only left the outer flaps of the box bottom, to which glue was applied in the same manner as seem previously, then they were folded inside and firmly pressed down for a minute.
The bottom box is now done!
Well, at least its shell is finished. We still have to work on the filling later on.