The Stock Exchange building can be purchased from the in-game Shop, from the Extras section.
This building allows you to win prizes. All prizes won are automatically added to your Storehouse.

You will get 1 free try for every day you log into the game. The Federal Reserve and National Bank buildings will increase the number of free attempts you have per day to 3.

Once you have used up all your free plays, you can either take your rewards and exit or continue playing for Megabucks. Each additional attempt costs 1 Megabuck. If you manage to get 100 points, you will get a 1000 Megabucks jackpot. To make sure that the points stack, you need to keep playing continuously without taking your prizes after each round. If luck is on your side, you can get some very valuable gifts this way!