Here's a nice worksheet with an answer key that focus solely on zero conditional type of conditional clauses. It aims to help students practice on sentence making with zero conditional clauses.
The exercise is simple but has a semi-controlled output. Students just read the situation and make sentences according to the condition described in the situation. The answer to each situation is single but can be expressed in various ways using the zero conditional form in the sentences. Although a suggested answer key is provided with the worksheet, you should be ready for various sentences that express a similar thought.
There's also consolidation worksheet on first conditionals, which might be useful if you want to compare the two clauses.