how to write a SKILL code for PCELL powergrid

Hi all,

I am new to SKILL coding. I am trying to create a power grid PCELL using SKILL. The user can switch on and off layers/vias depending on needs. I found some SKILL code online and modified to meet my need. Now, i can create metals (ex. M3) but I dont know how i can turn it on and off when the user checks on/off the checkbox on the 'Edit Instance Properties' window. please see my code below. 

procedure(powerGridPcell(cv "dnn")
let( (rectRodObj)

Nx=7
temp = 1
for(i 0 Nx
temp = 0.63 * i
rectRodObj = rodCreateRect(
?cvId cv
?layer list("M3" "drawing")
?bBox list(0:temp+0.125 5.04:temp+0.505)
)
);End for i

); let
); procedure

;; Create the PCell, the "drawing routine" is encapsulated in the
;; powerGridPcell function which does all the work

pcDefinePCell(
list(ddGetObj("test_rudy") "power_grid_pcell" "layout")
(
)
let( ((cv pcCellView))
powerGridPcell(cv)
); let
)

;; Create the CDF for the 'l' and 'w' parameters
let( (cellId cdfId)
when(cellId = ddGetObj("test_rudy" "power_grid_pcell")
;; if the cell CDF already exists, delete it
when( cdfId = cdfGetBaseCellCDF(cellId)
cdfDeleteCDF(cdfId)
)
;; create the base cell CDF
cdfId = cdfCreateBaseCellCDF(cellId)
;; create the parameters
cdfCreateParam( cdfId
?name "visibilityM3"
?prompt "M3"
?defValue "true"
?type "boolean"
?display "t"
)

cdfSaveCDF(cdfId)
); when
); let

Thanks