A sample code for a script tool which will have a single check box. If a check box will be checked by a user, the tool will verify existance of a specified data file.
import arcpy
input_fc = r'C:\GIS\Temp\data_shp.shp'
#getting the input parameter - will become a tool parameter in ArcGIS of Boolean type
ischecked = arcpy.GetParameterAsText(0)
#Important to convert the check box value to a string first.
#Should be 'true' with the small case for 't',
#not the 'True' as shown in the Python window in ArcGIS
if str(ischecked) == 'true':
arcpy.AddMessage("The check box was checked")
result = arcpy.Exists(input_fc)
#to return 'True' or 'False' depending on whether the data file exists
#since it is a Boolean, important to convert it to a string
arcpy.AddMessage(str(result))
else: #in this case, the check box value is 'false', user did not check the box
arcpy.AddMessage("The check box was not checked")
Remember to add a tool parameter of Boolean data type when creating a new script tool in ArcGIS Desktop application. This parameter will be automatically shown as a check box when user runs the tool.