一層【いっそう】
even more, still more, all the more, more than ever, one layer, lowest floor (of a building), rather, sooner, preferably
高層【こうそう】
high-rise (building), multistory, multistoried, tall, high (altitude), upper (atmosphere, air current, etc.)
階層【かいそう】
class, level, stratum, layer, hierarchy
上層【じょうそう】
upper stratum (classes, stories, storeys), upper layer, layer above