Create an "offline" exchange

My idea was to be able to sell and buy from another player anything even though he is not online.

In this server where I play, we have created a meeting point for the Market (Let’s say where is the theater, in the parking lots).
Unfortunately, I do not study codes, but I think that it is not difficult and I would like to try, maybe asking the basics that I miss and then step down to throw down something.

Owner:

  1. Marker to buy the space where you can put my stuff (As if it were a house, a store but in a free place).
  2. Become my possession, this space, to insert as if it were a “cash” the items in my inventory (weapons, fish, fruit, etc …)
  3. Having the possibility to choose prices. Maybe after adding the objects, a window with the newly inserted object comes out.
  4. Possibility to collect the goods. Then put it and remove it as you wish.
  5. In the list of actions that can be done, put another inventory where to insert the money as “objects” (similar to when they are storing weapons, or as dirty money)
  6. Being able to make those “clean money” -> normal money.

Opener:

  1. Climbed on the marker bought by me. The “phone” opens with just one word - Buy Goods - Or as in shops, the list of goods entered opens directly.
  2. As soon as the goods are bought, the money is scaled and made to become an object of the inventory and inserted in a cash box always of the space bought but only who owns it can see it.

(Also if you can, or someone can do something you could also use for gas stations. So if, for example, I buy a petrol station, I set my price and every day I go to recover the profits.)

Finally, I started with the first step: Create a Marker. What kind of guide can I follow?