Hi Sofie,
A couple of suggestions:
1) Limit the number of bricks for the tower building. give them the bottom and the top and tell them to choose only ten more. This will focus the building and might help to focus the stories too.
2) Give specific instructions (for example “tells us what you have built and what it says about you”) and stick to that brief. There will be time for complicated stories later. Also as mentioned by Rodrigo, state upfront some time guidlines if needed. If they are known to all you can assertively / politelty police them
3) I assume that Step 2 for you is Copy a model. If so, I keep this really simple, getting them to copy a simple 6 or 7 brick model (I usually pre-assemble it in the middle of the table). That means that copying is fairly quick.
4) I assume that Step 3 is modify the previous model (metaphorical jump for those who haven’t gone there yet). I make this an easy jump but always adapt it to be content relevant (even if only starting to open the subject). For example if the subject later is Team Life … this could be modify to represent the ideal or worst team member … This gives us an opportunity to already start addressing some of the “meat” as skills finishes and bigger questions loom.
Hope this helps and feel free to reach out to me if needed.
Alan.