Each worksheet is named for a month plus a data sheet and a roll-up sheet.
each month is just data with expenses of each project.

In the Roll-Up sheet I would like to pull information from one month at a
time using a lookup formula of the worksheet's name. BTW - on the roll-up
sheet I have a drop-down of the months.

My question is how do I write a formula that calculates the specific month I
choose and then returns the data from the matching worksheet? Using a
standard lookup function with variable worksheets returns an error message.