To change the given sentences into negative form, you can add the word "not" after the verb or use a negative form of the auxiliary verb "is" or "was." Here are the negative versions of the sentences:
1- It is not a good idea to work at night.
2- He was not making the bed. (or He wasn't making the bed.)
By adding "not" or using the negative form of the auxiliary verb, the sentences convey a negative meaning, indicating the opposite of the original statements.