The correct choice between "decide" and "decide on" depends on the structure of the sentence.
1. Decide:
- Use "decide" when it’s followed by a clause (subject + verb) or when the object is implied.
- Example: "They get to decide how their house is designed."
(Here, "decide" is followed by the clause "how their house is designed.")
2. Decide on:
- Use "decide on" when referring to /choosing/ or /making a decision about something specific/ (a noun or noun phrase).
- Example: "They get to decide on the design of their house."
(Here, "decide on" is followed by the noun "the design.")
Corrected Sentence:
"They get to decide how their house will look." (using "decide")
OR
"They get to decide on the look of their house." (using "decide on").