As a start I would like to obtain a design for the homepage, search results page, and individual item page. Based on those we can later add the design for the remaining pages.
The homepage should offer an easy way to search for sneakers. I think people like to search in 2 ways: via a search bar or via a search menu. I would create the search bar on top of the page, together with a dropdown menu next to it for "buy" or "trade" and maybe an additional dropdown box for size. On the left side it might be good to have menus per brand with further submenus for models (for this you can find inspiration on the flightclub and kixify website). The rest of the page can be filled with a flash for promos / sneakernews and a personal flash with recommended items / popular items / recently visited / watchlist. There should also be a clear link, somewhere on the homepage, for people willing to list an item for sale or trade.
The search results page should have the same the same search bar on top. I think the listings are best organised like on e-bay with filter menus on the left side on the screen to filter for Size, Condition, Shipping method, Brand, item location, price range, seller, ships to, etc. The top of the results screen should have filters for "All listings", "Auction", "Trade" and "Sneakx Store". People should also be able to filter on most recent, most popular, price + shipping.
The individual item page should again show the search bar on top of the screen. The page itself should show the title of the item, pictures, the bid/buy/trade fucntion (if applicable), the current price, whether or not the item is open for trades, a shipping table, his shipping/return policy, a feedback summary of the seller (number of transaction and positive feedback %), an add to watchlist function, links to share the listing on social media such as twitter, facebook, instagram, or via mail, and a contact seller function.
Every page on the website should also be social media friendly with a link to like or share on facebook, follow on twitter, follow on instagram or mail to.