A good topic sentence needs to introduce the topic to your reader, and grab their attention. I would start an essay about a dream house as "Imagine if your house could..." This would definitely catch your reader's attention! You could also start with a question, like asking your reader's what their dream house would be like. Writing the topic sentence is often the toughest part of the essay, in my opinion. Sometimes I even leave my topic sentence for the end - you might try this as well!