As readers progress into more complicated word patterns, boxes will grow. In the 5 letter box you can see that a reader of a word like this, will need to work with consonant blends and digraphs.
Materials to make Sound Boxes need not be complicated. You can draw one with a marker! Or, use colored tape to form boxes on a cookie sheet, then spell with magnetic letters. Or, use colored tape to form boxes on a table top, then spray shaving cream inside box parts for kids to write letters with their finger. Get creative. The methods are limitless. Go online and You tube some videos which demonstrate this strategy. You can also search the Internet for a variety of designs, including the cute one below from www.bogglesworldesl.com