You'll first need to add the organization to set a default discount and markup to an organization within your contacts list.
Once you've added the organization, follow these steps to set default pricing.
Step 1: Select the type "Supplier/Manufacturer"
Step 2: Mark the account as Trade or Retail.
Step 3: Enter your Designer Discount
Step 4: Enter your client Mark-up.
When you add an item to a project, the designer discount and markup will auto-populate within the item based on your pricing setting.
To learn how to set your pricing setting, see this article: Setting How Discounts & Markups Auto-populate