Adding the same resource to multiple items:
Select the items you want to add the resource to. You can select a continuous section by holding down shift and clicking the first and then last item (or the last and then first) or select multiple separate items by holding down CTRL and clicking on each of them.
Go to the Range menu, a submenu will appear below it.
Choose Resource, a popup will appear with your usual resource selection window.
Choose your resource by double-clicking it, or highlighting it and clicking Select
If you have multiple buildups on any of the selected items you will be asked which one to add the resource to.
The resource will now be against all those items.