You could log in to Google mymaps on a pc/mac with the email you used to use the phone.
Zoom in on your ware house as close as you can. Click creat new map. Name it Warehouse or somthing you remember. Use the Icons at the top of the page to "draw" section or areas in your warehouse over the warehouse.
When done click save and go to your phone. Turn on GPS and turn off use wireless location. Check your google maps on your phone. If you have the new Maps, click on layers, more layers, my maps. Click on warehouse or what ever name you used.
If you dont have the new Maps from google, download mymaps editor from the market. You can even use that in real time at the warehouse. It does the same as the web based google mymaps.
Hope this helps.