Build a csgo gambling website

I want to make a csgo [Steam game] betting website. The way it'll work is you'll click a button and it'll open a new page with a trade offer to be sent to a bot. You put in any amount of items that are worth above 2$. After the bot accepts the trade offer, the price of the item will get added to your "bank." With the money you have in the bank, you will able to select a price and what percentage of a chance you will have to win. You will be able to then choose an item that was traded to the bot and it will take away the amount the item is worth from the bank. The person will get a trade offer from the bot with the item and that's that. Whatever odds you choose will obviously affect the payout. I want to take a 2% cut on each of the bets.