How can I add a Checkbox to my form?

I want to add a label with a checkbox to indicate that a task has been completed, ie..

[checkbox] Have files been deleted

The checkbox will either be checked or unchecked.

I cannot seem to find a way to do this with the widgets and there is nothing available in the basic tab.

Any advice appreciated

The field you're looking for is called MULTIPLE CHOICE. You can find this field by clicking the ADD FORM ELEMENTS button > go to the BASIC tab > then scroll down until you see MULTIPLE CHOICE.