Maybe....I am not clear about ”かもしれない”

Usage:
Non-polite form + かもしれない
これは わからないかもしれません。
My question is : how to use it with negative noun, negative i-adjective and negative na-adjective.
1.あのひるは ﾃﾞﾊﾟ-ﾄじゃ ないです。→ あのひるは ﾃﾞﾊﾟ-ﾄじゃ ないかもしれない。?
2. あそこは 熱くないです → あそこは 熱くないかも しれません。？
3.あのホテルは しずかじゃないです。→ あのホテルは しずかじゃないかも しれません。？

For past tense, I should also use the non-polite form of a verb, am I right?
eg. 高かったかも しれません。？
Can kind Toritobe san or someone check my answers please. Thanks.

"Building" is ビル, not ひる.

What do you think the definition of non-polite form is? It only refers to verbs, present forms or affirmative forms? That's the answer.

Toritoribe said:

"Building" is ビル, not ひる.

What do you think the definition of non-polite form is? It only refers to verbs, present forms or affirmative forms? That's the answer.

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Thanks for the correction. If non-polite form refers to all including past tense then my answers should be correct.

Yes, except a fact that 高い is an i-adjective, not a verb, in your example. It also applied to negative past.