Instructions
Visit the Roblox website and log in to your account.
Scroll down your user page until you reach the "Stuff" box.
Click an item you've created such as a T-shirt. If you haven't created an item yet, click the "Create" link at the top of the "Stuff" box, click "Browse" on the new "Upload Texture" window and then navigate and select your texture file. Finish the creation process by clicking the "Create X" button, where "X" is the type of item.
Click the "Configure this X" link on the item's page, where "X" is the type of item.
Enter a name and description for your item, select a "Genre," click the "Sell this Item" check box and then type a price to sell the item for. Items can be sold for tickets or "robux," which is Roblox money. The marketplace has a 10 percent fee for selling items. Consider setting a low price since you're selling the item to your friend.
Click the "Update" button. The page should reload and display "Your changes to the item have been saved" along with a time stamp.
Sell the item to your friend by having her visit the Roblox "Catalog" page and clicking the category of your item. Tell her to look in the "Recently Updated" or "For Sale" area until she finds your item. She should click the item's name and then click the "Buy" button on the item's page.