For a while Rainbow has wanted to build a Ninky Nonk and was collecting equipment. Then eventually one day I had the useful box out and she set about building her Ninky Nonk while I built a cave that I'll show soon. We don't do a lot of useful box construction as she's still a little young. In the past I've had to ask a lot of questions to help her. Initially about the thing she was building, the parts of the thing, the objects in the box that resemble the part, where she was going to join it.... I would then suggest how to join in and help her do so. Very Vygotsky "zone of proximal development" - learning happens in the gap between what children can do alone and what they can do with assistance.
This Ninky Nonk project was a lesson in not interfering in my daughter's learning.
I jumped in and offered to join two carriages (with a pipe cleaner) which she accepted but then I watched her devise her own way of joining the next two carriages with sticky tape.
I offered to cut a door in one carriage which she accepted only to watch her load her Pontipines through her own door (the lid of the container).
The ability to stand back and let my children own their own learning is a challenge I face as a parent.
You might be interested in this article about not limiting your child's learning from the thought provoking White Oak School.