1. Log into your Google Affiliate Network account using the address: www.google.com/ads/affiliatenetwork.
2. Select the 'Links Beta' tab.
3. Click 'Switch to classic version' option at the top of the page.
4. Select the 'By Advertiser' option on the left side of the screen.
5. Locate the advertiser in the list for which you'd like to build a custom link.
6. Click the 'Build Your Own Links' option from the 'Actions' drop-down menu beside the advertiser of your choice. A pop-up should open of the advertiser's website.
7. Find the link you want to use for your custom link in the advertiser's website and copy it and the other necessary details into the 'Build Your Own Link' screen in your Google Affiliate Network account.
8. Select 'Build Link' at the bottom of the screen to display the link you created.