You may find that with an ancillary question, you only want the price to apply if the job meets a certain criteria. You can use IF statements to apply these types of pricing rules, using the range of functions available.
The syntax for IF statements is: if(condition, then, else) and these statements can be input in place of numerical values. 
As an example, you may charge £20.00 to fit each roof panel if the roof is glass, whereas you may not charge anything for fitting of polycarbonate sheets.
- There is a function named isglass – this is a Boolean type value, which returns a true or false value.
- There is a function named RoofSheetCount – this returns the number of roof sheets, that you’ll then multiply by £20.00 to calculate the total glass fitting cost.
1. Set the question as an automatic charge
2. In the Price tab, type: If(IsGlass, 20* RoofSheetCount, 0) In plain English, this reads as “If the roof material is glass, then apply a cost of £20 for each roof sheet. if the roof material is not glass, apply a cost of £0 ”
If you apply a fixed charge of £100 to fit polycarbonate, instead of £0, simply change the 0 at the end of the statement to 100 – I.e – If(IsGlass, 20* RoofSheetCount, 100)
In plain English, this reads as “If the roof material is glass, then apply a cost of £20 for each roof sheet. if the roof material is not glass, apply a fixed cost of £100 ”
If you apply a charge of £10 per polycarbonate sheet for fitting, you could change the statement to: If(IsGlass, 20* RoofSheetCount, 10* RoofSheetCount)
In plain English, this reads as “If the roof material is glass, then apply a cost of £20 for each roof sheet. if the roof material is not glass, apply a cost of £10 for each roof sheet