all you need to make a map is pencil, ruler and paper. And maybe a compass (the kind for drawing circles) if you really want to go crazynuts.
Sorry, it drives me a little bit more bonkers when people call fields "maps." This is not a video game.
seriously though, start on paper. think about the time, tools, materials and resources you have. Start creating something. Then ,adjust it after playing on it or even just walking through. You and friends can even ghost play--no need for paint or guns, just point your finger and say pew pew pew. A crappy plan is better than no plan at all--you can always adjust/redesign as you go along. Personally I am a meticulous planner, but inevitably you will encounter things in the execution of your plan that you did not forsee on paper and you will need to adapt. You can always improve/adjust as you go. Employ the advice and manpower of people who actually play on the field.
Do not expect to do a google search to find a just right design pre-made for you. Look at existing fields/video game maps/historic battles/etc on the internet & books (those things filled with paper) and especially in person to gather ideas, design concepts and components. Do not just copy and paste something, unless that is exactly what you want to play. Think about sun light, prevailing wind directions and other factors at your site. Make it your own. It will take work, but it will be rewarding. Best of luck. Let me know if you need any other ideas/input.
Edit: Overlord has a valuable point: borrowing from real life, can be interesting and product. BUT, if your field directly mimics real life, especially recent events, it may send the wrong message and put some people off.
Edit2: looked at the embassy pic. looks like it would create a lot of static play with people bunkering up/moving very slowly.