the best way to make an outdoor scene is slowly, with lots of attention to detail. keep polys to an absolute minimum and work from where the player starts in the map outward. build segments and place entities at the same time. this will keep the map detailed.
needless to say, the minimum system specs for a good frame rate will rise when making an outdoor map. a good idea is to keep it as close to an indoor map as possible. the more linear, the better. to keep framerate high, here are some tips:
cut down on unnecessary enemies. instead of placing 2 bad guys, spawn 2 of 1 bad guy.
block the players view whenever possible, this gives the engine a chance to not render things that are really far away, or unseen.
keep the player from getting "high" up in the level. if that happens, the frame rate will drastically slow down when the entire level is in view. (FPSC has no LOD system)
keep background objects to a minimum. although it can be a little more boring, sometimes it's better to block the player's view with a wall than it is to have a million polygons of things the player can never reach.
use a mod. fenix mod, now with horror mod can not only boost FPS rate, but can also allow changes in the player's field of view, making your map look bigger.
to fenix mod!