The mystery knit-a-long begins

I worked in day care centres for many years: the toys were very cool! : ) The person who invented building blocks is a genius. Interlocking blocks that could become anything your mind could dream up: hours of fun.
Interlocking blocks: this is how I would like you to think of this knit-a-long. I sill supply you with a series of interlocking steps and then give you lots of room to "play". How do you play? Simply by making a series of choices. Delightfully we will work together to "design" "what ever you are knitting".
Let's begin, shall we? I trust you have the requested yarn and knitting needles. I asked you to acquire 540 yards of yarn. I would advice you to have one more ball just in case. That old boy scout motto: be prepared.
The first decision to make is to select a stitch pattern. You will find a number of posts to aide your decision: March 21st, 22nd, 23rd, 24th, 25th, 26th, 27th, and 28th as well as April 2nd. I will wait here while you make your choice.

Block A (make 4)
Cast on 25 stitches work in chosen stitch pattern for five inches. Cast off.

Tip: Do you have posted notes? If so use them to mark each block with an "A". You can also do this simply with a pin or tape and a scarp piece of paper. I can not stress enough that it is very important that you keep track of your blocks. I will be referring to the blocks as "block A" etc. So please, please, please mark them.
I will supply you with the next line next Saturday (April 15th). ...until then happy knitting!

Tomorrow: frankly, I'm not sure. So it will be a nice surprise for both of us. : )