Ok, first step, The Board. The playing space we have on the tables at the College is about 1200 mm by 1200 mm. The bases of the figures are about 20 mm wide which, including space for enthusiastic fingers, requires squares in corridors to be about 30 mm wide. This is good as models such as the power-loader, Alien Queen and most aliens have tails, claws etc that poke over the side of the base. It also allows models to move/ shoot past each other.
I also wanted to include air-ducts for the models to crawl through as well. This will allow for another aspect of the game and provide the Aliens side with cover and maneuvering options. Marines and predators will be able to use the ducts too, but a a greatly reduced speed.
The boards will need to be interchangeable in order to provide a little variety in the games. Similar to Space-hulk with corridor sections and rooms. I was thinking of 300 mm square boards to begin with. However, I settled with the idea of smaller boards and corridors as they provide real alternative layouts for the missions. With this in mind I have designed the boards to be in multiples of 3x3 square sections. Middle squares will provide open ways for movement, edges will have walls with a height of 40 mm to allow for the air ducts to be set at a higher position.