HI @mahadev.v
3rd Argument is ParameterType i.e which type of value you're going to save. (ex. Text,Number, Length, Area) use the
ParameterType Enum for this.
Reference Code:
Document doc = commandData.Application.ActiveUIDocument.Document;
using (Transaction createGlobalParameter = new Transaction(doc, "Create Global Parameter"))
{
createGlobalParameter.Start();
//By using Parameter, use can able to fill only number
GlobalParameter param = GlobalParameter.Create(doc, "Demo Length Parameter", ParameterType.Length);
//By using Parameter, use can able to fill only Text
GlobalParameter param_02 = GlobalParameter.Create(doc, "Demo Text Parameter", ParameterType.Text);
createGlobalParameter.Commit();
}
Reference Output Image:

Hope this will helps 🙂
Mohamed Arshad K
Software Developer (CAD & BIM)