Explanation
Making polite suggestions; 'how about if', 'what if', 'it would be good if'.
Formation
Verb-casual, past + たら いかがですか, い-Adjective + かったら いかがですか, な-Adjective + だったら いかがですか, Noun + だったら いかがですか
Detailed explanation
The ～たら いかがですか grammar point is used to make polite suggestions, ask for opinions, or imply that something would be good or desirable if the condition is met. The formation differs depending on whether it is used with a verb, い-adjective, な-adjective, or noun.
Examples
Toshokan ni ittara ikaga desu ka.
How about going to the library?
Samukattara kaadigan wo kiru no wa ikaga desu ka.
How about wearing a cardigan if it's cold?
Heya ga kurakattara shoumei wo tsukeru no wa ikaga desu ka.
What if you turn on the light if the room is dark?
Jibun no iken dattara tanin ni kiku no wa ikaga desu ka.
How about asking others if it's your own opinion?
Practice
Grammar content sourced from hanabira.org.