Your WBS (Work Breakdown Structure) is nothing more than the breakdown of your final project deliverable into smaller and smaller pieces. Keep breaking down until you can accurately estimate cost and time (duration) for each sub-deliverable.
Try this. Get some open wall space and a lot of post-it notes. Write out the project’s main top level deliverable, for example “12 story office tower”, on a single post-it, and place it at the top center of the wall.
Now have your team write out everything single thing they can think of that will be needed to create such a tower, one thing (one deliverable) per post-it. Have them randomly place them on the wall. Have them start to place the alike thing together, and label the groups. For example, anything to do with heating could be grouped under “HVAC”.
(Ask them to do this without talking to each other. This prevents the verbal team members from dominating the non-verbal team members.)
If you like, you can start with those high level groupings first. This is easier when you have knowledge and expertise onboard from the beginning. and it speeds things along.
You should see the organic creation of the initial high-level WBS, appearing quickly on the wall. You will also see your team members interacting, learning from each other, possible building up some team spirit. You will witness cross-discipline thinking, and professional growth.
Plus – it’s fun to mess with post-its at work.