The Trading System is an awesome feature for Builders Club members that allows them to exchange Limited/Limited U items and Robux with other BC members. Both players will also need to have this feature enabled inside of the Privacy tab of their Account Settings page.
Creating the Trade
To use the feature, go to the profile of the player you wish to trade with. You can search for people by typing their name into the Search bar at the top of the Roblox website. Once you're on their profile page, click the button that looks like three dots in the upper right corner of the box that contains their username and friends/follower information. On the menu that pops up, select Trade Items.
After doing the above, a window will open showing the available items you and the player have to trade. Hover your mouse over an item to reveal either an Add to Offer button (your items) or Request button (their items) which can be used to include it in the exchange. You can also choose to sweeten the deal by including some additional Robux, but please keep in mind that there will be a 30% transaction fee removed should the offer be accepted.
Note: The amount of Robux cannot exceed 50% of the current offer, calculated after the transaction fee is removed. Example, if you offer an item that is worth 300 Robux, you cannot add more than 150 Robux--post transaction fee--to the offer.
Once you've built a trade to your liking, you can submit it. Submitting a new trade will notify the player via private message.
Viewing Your Current or Past Trades
A list of pending (inbound/outbound), completed, and inactive trade offers can be seen the Trade Type pull-down menu, located on the Trade page.
Accepting, Declining, and Countering A Trade
Viewing a pending offer opens a window allowing the player to accept or decline the trade. That said, if a player does not want to accept the current offer and wants to change it by asking for different or more items/Robux, they can choose to click the Counter button.