If you wish to work out a total rate for an item including materials, labour, delivery etc in BT2, you can double click in the Rate column against an item and then enter in all the costs associated with that item.
e.g. if you wish to work out the total cost to supply and fix a door to a building, you may want to include the cost of the door itself, some hinges, architrave, a lock and labour to hang it. Once you have entered all this information (See example attached), close the 'Rate" sheet and the combined total of all costs will appear in blue at the "Trade Items" level. Count up the number of doors on the plan and you will have a budget for supplying and installing the door.
NOTE: Create a template job with all of your common items that have composite rates. You can then copy the Job at the Job Manager screen so you don't have to build up the composite rates for every job.