Do I not use 'avez' with vous? vous-allez avez un lion
The construction for near future is relatively similar in English and in French;
"Aurastu un lion" is also right although they don't accept it. I think it's more grammatically correct seeing as it's a question and the inversion subject/verb is required.
In spoken language though it's largely accepted to ask "Tu auras un lion?".
In the inversion Verb-Subject, the hyphen is required: auras-tu ?