This is an option that is sometimes misunderstood in the house plan world. Let me explain what it is. The "Mirror Option" just mirrors the plan so that it is an exact mirror of the original floor plan. This puts the right side of the home on the left side and the left on the right. But when they do the mirror option the designer does not take the time to make all of the letters and numbers readable. This is why the option is usually free or at a very low cost. Now to use these mirrored plans you have to purchase at least one set that is not mirrored, just so you can refer to the readable version to understand the plans. This gets a little old and tedious fast. If you ask anyone who has built a home using the mirrored fashion, they most likely would never do it again. So, most designers offer a Right Reading Reverse Option. If you purchase your set of plans and ask for this option, the designer will go through and reverse the plans and make all of the writing readable. This is a great option that costs a bit extra, but makes having a reversed set of plans really nice.