all he needed was some empty plastic bottles. we don't usually have those on hand but were able to acquire some within a couple of days. (i learned about pbh that i needed to make sure this happened quickly, before he lost interest, and i made sure to do so this time.)
i was going to be away on the day he wanted to construct the rocket, so we asked if dad would be available. he was, and agreed to take some photos for documentation.
in case you would like to see the video that inspired him to do this, watch here:
now we are just waiting for a warm, dry-ish day so we can test it out.