a single function with different returns

[MattP]

Rather than creating your own class to return or having a ByRef parameter for the function I would advise you to split it into 2 functions. Each method should have a single responsibility.

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Const sqFt = 1000
        Dim gal = Gallons(sqFt)
        Dim cost = RoomPaintCost(gal, 19.95)
    End Sub
 
    Private Shared Function Gallons(squareFeet As Integer) As Decimal
        Return Math.Ceiling(squareFeet / 115)
    End Function
 
    Private Shared Function RoomPaintCost(gallons As Decimal, paintCost As Decimal) As Decimal
        Return gallons * paintCost
    End Function