If statements in Revit.

I have a storage rack family that I would like to have lower shelf height be the same as all the other shelves above. I also want to make the lower shelf another height if it is considered a bridge (drive through area below it). I used an if statement along with a yes/no parameter. So how this works;

Parameter Type       Parameter
Yes/No                   Bridge (B)
Length                     Shelf to Shelf Ht (SSH)
Length                     Bridge Ht (BH)
Length                     Lower Shelf Ht (LSH)

LSH = if(B,BH,SSH)

Simple terms if (B)Bridge is checked then it uses parameter or info after first comma (BH) or Bridge Ht, else it will use the info after the last comma (SSH) or Shelf to Shelf Ht. “IF(condition, what happens if true, what happens if false)”