屋根

How it works

の (of) links two nouns to show possession: その家(そのいえ) (that house) owns the 屋根(やね) (roof). Then は (topic) lifts that roof as the topic, and the adjective 赤い(あかい) (red) sits at the end as the whole description — i-adjectives like this can finish a sentence by themselves, no “is” needed.