Cirrus clouds are found around 18000 feet so I guess if the devs should add this cloud type, they should probably make it similar to a haze effect since these types are thin and wispy clouds. They can be simple cirrus (thin, icy wisps), cirrocumulus (puffy), or cirrostratus (flat, sheetlike clouds).
Status clouds are quite easy because it is similar to the haze. These type of cloud is found in different altitudes varying from high level (above 20,000 ft.), middle level (6,500-20,000 ft.), and low level (below 6,500 ft.).
Nimbostratus are dark, low-level clouds accompanied by light to moderately falling precipitation. Low clouds are primarily composed of water droplets since their bases generally lie below 6,500 feet (2,000 meters). However, when temperatures are cold enough, these clouds may also contain ice particles and snow.
Puffy, evolving rain clouds are Cumulonimbus. These clouds can evolve into thunderstorms.
Altostratus (a flat cloud covering) or Altocumulus (white, cottony clouds) are between 6,500 and 18,000 feet.
Stratocumulus look like mounds of whipped cream or cotton.
I wish these can be modeled to allow for more realism. Though I guess modeling these cloud types would be a real FPS killer.