At what task level can I assign project assets?

You can assign project assets at either the top or bottom task level in a project. You can't assign assets to any mid-level tasks.

What are top, bottom, and mid-level tasks?

Consider the following project plan:

Task 1.1 in this screenshot contains five child tasks. Four of these tasks are associated with clay tennis courts, while the fifth task, 1.1.5 Clay Tennis Courts Common Costs, is dedicated only to collecting common costs associated with the four clay tennis courts in the Task 1.1 summary task. For example, common costs associated with clay tennis courts could be clay, stones, tennis nets, and so on.

Similarly, Task 4.0 in the screenshot is dedicated only to collecting common costs associated with the creation of the tennis club itself. For example, you could have common costs associated with electrical and plumbing, permits, land costs, architectural design costs, and so on. Just to clarify, common costs for the clay required for the four tennis courts would NOT be captured here; these would be captured in Task 1.1.5. All common costs collected in 4.0 will be allocated to project assets and 1.0, 2.0, and 3.0 summary tasks, because these costs must be borne by each of these assets.