It was once a fire station later converted into a museum, but it looks like a red barn to me.
This is such an interesting sentence! I hope you use it in the essay.
Did you google "descriptive essay" to see explanations of how to do it? It is all about imagery words. That mens not only words that make the reader see something (i.e. red barn), but also words that convey texture, smells, and even emotions you feel when standing in front of the building.
350 words is going to be 3-4 paragraphs. Start with a very interesting sentence, and end the 1st paragraph with a sentence that you would use if you were required to write the whole essay in one sentence (the thesis statement)
You will have 2 body paragraphs, so think of a topic sentence for each. Google "topic sentences" if you don't know what they are.
Write a conclusion paragraph that elaborates on that main idea from the thesis statement. Give a good, thoughtful, descriptive presentation of the building.
:-D