I suggest making pentominoes out of alphabet blocks. They are so much more interesting because you can build with them. That and you can try to solve for the 2 x 5 x 6 shape or the 3 x 4 x 5 shape. :-)
Step 1: Gather Alphabet Blocks
You will also need glue and rubber bands.
Step 2: Get to Know Your Pentominoes
F, I, L, N, P, T, U, V, W, X, Y, Z.
The way to remember the letters is the nonsense word, "filnop" and the end of the alphabet, T through Z.
Here are the first five shapes/letters:
Step 3: The Next Seven Pieces
Step 4: Glue - Start With the Easy Ones
For the "L" - Line up four blocks, glue and wrap them with a rubber band. Add one block on one end to make the "L."
For the "Y" - Line up four blocks, glue and wrap them with a rubber band. Add one block onto the block next to the end.
There is only one "gotcha" in this. When you get to the "U" piece, make sure you make it wide enough so that another piece will fit in it. Or you can sand it down after it is all glued, but why bother. Just make sure the space is big enough.
Repeat creating each of the twelve pieces. Put them away to dry overnight or so.
Step 5: Playing With the Pentominoe Pieces
1 x 6 x 10 - 2339 solutions (not counting rotations and mirror images)
1 x 5 x 12 - 1010 solutions
1 x 4 x 15 - 368 solutions
1 x 3 x 20 - two solutions
2 x 5 x 6
3 x 4 x 5