User Input before Create

Hi Team, I have the below requirement to get user input and based on that need to create a part. Example:
  1. I should have a drop down list to get user input (On Click of create new Part)
  2. Based on the select value from drop down list, I need to set that value in Part window
How to achieve this. I'm new to ARAS development.  
  • Hi Sebastian I created a custom form and added to Item Type as Client Events to get user input. It has a drop down list , Create button and Cancel button. I'm trying to get the value which user has selected and pass that to another form. How to achieve this. var producttype = document.thisItem.getProperty("input_type", ""); alert(producttype); On Click of Create button gives the below error Event handler failed with message: TypeError: Cannot read property 'getProperty' of undefined