V-masu stem / い-adj -い / な-adj + そうだ
looks like, seems about to
Your own impression from looking. Attaches to the *stem*, not the plain form. いい becomes よさそう and ない becomes なさそう — irregular, and regularly tested. Never used for things you can see plainly: you don't say 赤そうです about something obviously red.
このケーキはおいしそうですね。
この ケーキは おいしそうですね。
This cake looks delicious.
今にも雨が降りそうです。
いまにも あめが ふりそうです。
It looks like it could rain any minute.