1.他的房间太不干净了 means, his room is very dirty. 2.他的房间不太干净了 means, his room is a little bit dirty

1.他的房间太不干净了 = 他的房间太脏了 ＝ His room is EXTREMELY dirty. = How dirty his room is. 2.他的房间不太干净 = His room is not very clean. BTW: It's incorrect to append 了 to 他的房间不太干净

前面一个意思深一点，后面一个意思浅一点。就像 you are so beautiful!!! and you are beautiful.

程度不一样，第一个程度深，第二个程度浅

1.他的房间太不干净了 means, his room is very dirty. 2.他的房间不太干净了 means, his room is a little bit dirty