Please, correct my sentence

是可以的，但記得在reported speech也要依照其他敘事文的規則，如時式要一致(Sequence of Tense)，若是要間接敘述法出現，則要注意，主要子句的動詞為現在時式時，從屬子句的動詞就不受限制，但若主要子句的動詞為過去時式時，從屬子句的動詞，必須是過去時式，或過去完成時式。

所以你以上的句子，應為

He said that he had found a piece of reflective paper stuck on the wall while he had been cleaning the floor.

(其實stuck on the wall，這個己經是形容詞片語，毋須用had been stuck on the wall）

2006-12-04 11:50:25 補充：
為甚麼要用Past Perfect tense，若我們將它主要子句轉為現在式時，大約是He says that he found a piece of reflective paper stuck on the wall while he was cleaning the floor.所以，我們看到在主要子句為現在式時，從屬子句也是過去式，所以當主要子句為過去式時，從屬子句就要用過去完成式和過去完成進行式（在一般的情況下）

It should be changed to:

He said that he found a piece of reflective paper stuck on the wall while he was cleaning the floor.

or

He said while he was cleaning the floor, he found a piece of reflective paper that stuck on the wall.

He said that he found a piece of reflective paper stucking on the wall while he
was cleaning the floor.
You canstill use past continue tense.