I understand it will be an interesting exercise in machining and should be fun to make. However, decent commercial crank pullers (like my Shimano TL-FC10 or Park's equivalent) are well made, properly heat treated and will outlast you and your children so you aren't gaining quality or durability with your home made one, just the satisfaction of doing it yourself. That alone may be worth the effort.

Here is Park Tools CW7 crank puller that you can use for ideas and as a model for your puller: http://www.parktool.com/product/univ...d-cranks-cwp-7