What you plan to add. These raise the appraisal and get charged to the rehab, so you can see whether they pay for themselves. Above grade counts as living area and is compared straight against the comps. Basement never counts as living area — an appraiser puts finished below-grade space on its own line and pays a fraction of the above-grade rate for it. It is also far cheaper to build, since the shell is already there.
Leave blank to use what the data source reports. Fill these in when the listing is off-market or the public record is wrong.