The contract for the building of the north aisle at St James’s Church, Biddenham, Bedfordshire, in 1522 is an exceptional document that escaped the surveys of L F Salzman, John Harvey and most later scholars. Unlike other surviving medieval building contracts, it is the rough draft of an indenture, showing the alterations and changes that were made before it was copied into a neat final version and sealed. By surveying these changes it is possible to delineate, for the first time, the process of negotiation engaged in by its patron, Sir William Butler, and the mason, John Laverok. Unusual too are the details it provides of Butler’s collaboration with the parish in building the well-constructed aisle that would bear his arms. This went further than simply defraying the cost of the work, and is of significance for our wider understanding of the organisation and financing of parish church construction in the sixteenth century. Most importantly, it demonstrates the breadth and complexity of forms that co-operation could take between gentry and parish, and shows that projects with the arms of a single family could nevertheless be funded collaboratively.