Step 3: Glue flaps together

Start with the 30 AAB triangles.  Taking 5 at a time, glue the short sides of them together to form a pentagon.  You should end up with 6 of these pentagons.  If you measured and cut right, the pentagons won't be completely flat.  Be sure to keep all the flaps on one side.

The exposed edges of the pentagons should all be the B  measuring side, 12 inches in this case.

Now glue one of the BBB triangles to a side of a pentagon.  Glue another pentagon to another side of that BBB triangle to end up with something like picture 6.

Let's say the exposed edge of that BBB triangle is the bottom of this piece.  Glue another BBB triangle to one of the pentagons so that its exposed edge is also at the bottom.  Keep gluing pentagons alternating with BBB triangles so that one edge of each pentagon and one edge of each BBB triangle line up in a sort of gently curved bottom (like in picture 7) until you have 5 pentagons and 5 BBB triangles.  

In my case, I only used 4 BBB triangles here so I could leave the top of the door open.

You should have 1 pentagon left and 5 BBB triangles left.  I had only 3 BBB triangles left because I wanted to leave two windows in the dome.

Stand the line of glued pentagons and triangles up so that the bottom is resting on the floor.  Bring the ends together to form a circle like in picture 8.  In my picture, the open triangle is the top of the door.  You might decide not to leave an open triangle.  Notice that instead of seeing pentagons in this structure, you could see hexagons with one top piece missing.

Glue the BBB triangles, point down, into these spaces.

Now there should be an open pentagon shape at the top, ready for you to glue in your last cardboard pentagon.

I'm really sorry for not having pictures of that part; it seems that Lilith got into my photos and deleted some when I thought she was simply playing Tozzle on my iphone.

Now glue a square along the edge of each exposed triangle edge at the bottom of the dome.  This will raise it B unites above the ground, 12 inches in this case.  Glue the sides of the B squares to each other where they touch.  Once again, make sure to keep all the flaps on the same side.  Some people keep them on the outside, but I wanted mine on the inside.  Whichever you choose, be consistent.

If you want to reinforce your structure, cut extra triangles and squares to match up with the ones you have, but without flaps this time.  Glue the shapes without flaps to the shapes with flaps on the outside (if the flaps are kept on the inside).  This will make a double layer of cardboard for the structure, but not a double layer for flaps.  This works best if you keep the grain of the cardboard perpendicular;  have one piece with a vertical grain glued to one piece with a horizontal grain.

That's a lot of extra work, though, and probably not worth it.  I reinforced the squares this way, but not the triangles.  Note in the last picture, the square at the edge of the door has one exposed cut edge along with a flap.