Let's create a screen with a cave shop similar to the ones in the original The Legend of Zelda.
Go to Screen 66 (one screen up from Screen 76) and draw the following screen. Make sure to use Cave (Walk Down) [A] for the cave combo.
This screen is where our maze path from the previous screen exits. You don't have to worry about setting up connecting screens for the other two directions of the maze screen since it's not possible to access those areas in this tutorial.
Now let's do some screen setup. Shops are mostly set up the same as any other cave screen, so let's cover the basics of that again.
Setting up the Cave Information
Everything so far should end up looking similar to this (including the screen info):
From here, things will diverge as we set up the shop specific stuff. Go to Quest→Misc Data→Shop Types
Select Shop Type 0 and press Edit.
Enter a name for this shop type so that you can find it easily in ZQuest. After that, select items for the shop and enter their prices. Previews of the items will be shown to the right.
Note: While you can enter just about anything in a shop, it's recommended that you at least include bombs and a candle in this particular shop for the sake of future screens.
When you are finished, press OK then press Done on the Shop Types select.
Now go to Screen→Room Type (or press R) and set it to Shop.
Go to Screen→Shop Type (or press A) and set it to the shop type we just created.
And there you have it. The final screen in ZQuest should look similar to this:
Note that the Screen Info should actually be showing you the items for sell in the shop.
The shop should look like this in Zelda Classic: