I make a lot of altered art but this scrapbooking technique works for both altered books and scrapbooks. You can add as many flips as you can fit on your page and the only restrictions as to the actual size is that the parts that flip fit through the bottom cross piece. Also, you may not want the pull section at the bottom to extend out of the book because then you cant stand it up without damaging it.
Step 1: Once you know the size you want to make, cut all the pieces you will need from cardstock. If it is too flimsily, the flipping action wont be smooth and it will be harder to retract.
Step 2: Take the 8-1/2 x 2 piece and mark one end at Ύ intervals so that you will have four sets of marks. Score each mark and fold paying attention to keeping the edges even.
Step 3: Mount your images onto the 2 squares and then mount that onto the 2-1/4 squares. You could also stamp images or words if desired.
Step 4: On the side with the mountain folds (they stick up) apply glue across all four sections. Starting with the inside most section, fold it so that it stands upright and attach one of the squares, watch that it is even with the bottom of the fold and equal on each side. Then continue to fold on the next section, add the next square matching its edges to the first one, etc. until all squares are added.
Step 5: Apply glue to the edge of the last square and glue it in the center of the 1 x 4-1/4 crosspiece. This piece will not flip but remains attached to the crosspiece.

Step 6: You are ready to put it into your spread. I suggest your use something that will hold it firmly. Tape and/or glue are really not sufficient. I like eyelets, staples or nail heads for this.
Hope this scrapbooking technique adds a bit of fun to your next layout!
Find more scrapbooking techniques here.