Learn Russian: Они не прочитают наш лозунг, даже если мы сделаем большой плакат. - They won't read our slogan, even if we make a big poster.

We use the indicative because this condition is treated as a real possibility. While it is hypothetical, the speaker considers making a big poster a realistic option for the future. If it were entirely counterfactual or highly unlikely, you would use the subjunctive with бы and the past tense.

In English, we say "even if we make" using the present tense. Why is сделаем in the future tense?

Russian is stricter about tense logic in conditional clauses. Since the action of making the poster belongs to the future, Russian requires the future tense in the даже если clause. English, by contrast, shifts to the present tense for future conditions.

Could we use the imperfective forms (будут читать, будем делать) here instead of the perfective прочитают and сделаем?

Using perfective verbs highlights the completion and the result of the actions. Сделаем means we will successfully finish making the poster, and не прочитают means they won't manage to read it. The imperfective would awkwardly focus on the ongoing process, which doesn't fit the intended meaning.

Are наш лозунг and большой плакат in the nominative case here?