Out of interest I have tried to do a field design based on this site, using the information available on the planning portal. Particularly I wanted to test whether the very linear layout of the existing mall could be made into something more playable. So I tried to implement some theories from video game level design and see if they can be applied here.
The below is an illustration of a possible design and the steps I had taken.
Step 1 Design preparations
First we need to allocate space to the safe zone and game zone etc.
There are two main existing entrances to the mall but the escalators to the south in my opinion will not be suitable because they cannot function as stairs nor fire escape, so if they are permanently turned off this entrance cannot be safely used. Therefore we can only use the north entrance as the main entrance, accordingly the safe zone (and its size requirement for 50 visitors) is placed next to the entrance lobby.
The lobby has enough space for a small reception and waiting area and probably even a small shop. Staff and guest toilets are upstairs from the safe zone.
My design is heavily based on the concept of "lanes" in game level design which refers to the overall pathing network of the map. The immediate issue is too many dead-ends, which is an absolute nono in level design, so before we can even design anything we need to eliminate these dead-ends by creating loops. This is achieved by demolishing the existing partition walls (where structurally permitted) to create openings near the end of these dead-ends, so they can continue their paths and loop back into the map. At the bottom space where it is only reachable via a choke point, I have walled off the path to effectively create another loop that can be meaningfully progressed from one side through another.
This becomes the basic "topology" of the map that we can start to work on.
Step 2 Topological interventions
Looking at the topology it is immediately obvious the central lane is too connected and will attract too much action from everywhere, in game level design terms this is too many options for the player to choose from. Three precision cuts can prune this network into several distinct sectors with an acceptable number of optional paths to progress through.
Due to the shape of how this is arranged, it seems natural to place the two team spawn points on left and right, so there are multiple optional sectors and paths for them to fight through. If the spawns are top and bottom it would appear too much choke points will be in the middle and the winding paths near the two spawns will not see too many action therefore wasted space.
Step 3 Cover placement and distances
With the schematic from the previous step we can start to sketch out where to put the covers and checking the distances.
At this point I was only concerned with the gameplay itself and not think too much about scenic design, which will come later. For example I am only placing the high or low covers based on how the space can be progressed through, and trying to have a variation of tactical options for each situation. For areas near the two spawns I would also try to give advantage to the home team to try to help them progress back towards the middle.
There are 4 Point Of Interests (for objectives) placed in each zone, and by measuring the distances from each spawn their positions can be tweaked for balance. By happy accident only two can be balanced and the other two is giving each of the team a slight advantage, which should be good for various game modes (e.g. bomb diffusion).
This is also when fire escapes distances could be checked to make sure at every point from the map there is a suitable escape route for fire safety reasons and compliance with regulations (drawing illustrative only, not fire safety advice).
(Disclaimer: This post is not professional advice. To comply with building regulations and dealing with planning conditions and other stuff please consult professionals.)
Step 4 Scenic design
Once we have the schematic of roughly how the tactical gameplay is conducted, we can start to make it pretty and immersive. The four "sectors" of the map makes a good template for different biomes or themes to take place. In this example I have made up some themes like "Mall" and "Factory" and "Office" and "Airfield". This can then guide how we can choose what objects to put up as cover, and what kind of non-functional decorative doodads to put up on walls and so on.
For example in the "Mall" each of the rooms can be a different vendor with different themes e.g. restaurant or fashion shop or phone shop etc. which influences the atmosphere or feel or even distribution of covers of each space.
Again for example the "Factory" can be heavily decorated with fake pipes or barrels. And in the "Airfield" with decorations associated with an airport like check-in counters or duty-free shops and so on. Notice I have put the "Airfield" to the south area to make use of the high level of natural lighting to suit the atmosphere, and the "Factory" in the middle so it is darker.
Step 5 Detail designs and construction and so on (no image)
The remaining steps are just realising the interior design, prop design, signage placement, lighting, etc. to generally follow the themes of each zone or room. I don't have a drawing here because this can be heavily influenced by the aesthetic taste of the business operator and their budget and so on.
This is also where the practical and safety details to be added like fire escape signage, or transitional thresholds from safe zone to game area, or special floor markings etc. In this example there may also be visibility concerns because the glass curtain walling to the south (facing the high street) may need to be blacked out to prevent pedestrians from seeing the RIFs, so is the entrance lobby to the north.
In terms of construction, the decorations and covers and props and other doodads can be simple pieces of woodwork or metalwork. There could even be interactive elements e.g. electronic or manually operated installations. It can be really creative and use savaged car parts or heavy machines and so on as cover or decoration. Once construction is complete and the necessary props added, the site should be functional and playable and rest is getting outside of the scope of map design.
In conclusion, this is just a sketch exercise for me to dabble into airsoft field design but I think this map that I have drawn should play fairly well and look fairly immersive given some creativity and budget. Any criticism and suggestions are very welcome.