Referencing External Workbooks?

I'm trying to set-up a costing system as follows:

Each job has it's own xls file, this is a list of manually input costs and a total cost at the bottom (total is the same Cell reference: G24) for all xls files. The xls file is named the same as the job - F0001, F0002 etc.

At the end of every month we then want to create a master list xls file for all jobs being invoiced that month. This is a list of all the jobs - F0001, F0002 etc. In Column A, and the corresponding cost totals in column B.

In the master file we want to be able to type in the job reference to column A (i.e. the file names of the single job files -F0001, F0002 etc) and have the corresponding total for that reference display automatically in Column B (i.e. Cell G24 from file F0001 will display in the master file cell B1, when 'F0001' is typed in cell A1).

Ideally the master file would display all the individual entries automatically, so no need to input the job references either - simply scanning the directory for the other files present and creating a list automatically in the master file, alternatively it can get the job reference from Cell A1 in the individual job files, instead of from the file name.