[subject] + 多 / 多么 + [adjective] + 啊
多 / 多么 + [adjective] + 的 + [noun] + 啊
[subject] + 多么 + 希望 / 想 + [verb phrase] + 啊
多 or 多么 before an adjective, with 啊 at the end, makes an exclamation: "how …!" or "what a …!". 多 is the everyday form; 多么 is fuller and more emotional, and the one you'll meet in writing.
The adjective stands bare, with no 很.
啊 often changes to 呀 after a vowel: 多好呀.
多 / 多么 + adjective + 的 + noun + 啊 is "what a …".
多么 also goes before verbs of wanting, 希望 and 想.
多 + adjective without 啊 asks "how …?" – 他多高? asks his height. With 啊 and the falling tone of an exclamation, 他多高啊! marvels at it.