Here's a low cost thought: Print out photocopies of this house, look though Houzz for ideas, buy colored pencils and mark up the photocopies. Here are brick exterior homes https://www.houzz.com/photos/brick-exterior-home-ideas-phbr1-bp~t_736~a_32-223

Thanks! I've sketched some stuff out on paper already, but I was thinking that if I had some kind of software I could better determine how much square footage I need to add for a master bath, walk-in-closet, garage, etc. I have several ideas on how to lay rooms out, but I'm not sure which option will be our best.

Try Icovia Space Planner, really better for individual rooms but worth a look. Hope that helps. Charmean Neithart

Vicki,
Before you embark on designing the addition, make sure you understand the zoning requirements for your community. You may find minimum sideline and rear requirements that restrict the size of the addition or require you to apply for a variance. You should also collect any plot plan documents you have to take with you when you do choose an architect. If no plot plan is available you will have to have the property surveyed...$$ If there are house plans kicking around they will be helpful to the architect and builder you choose. As a builder north of Boston, MA my advice is to start looking for a builder at the same time you are choosing an architect. The best situation is to have the team building the addition part of the design process. And for the interior space you may only need a good builder/remodeler. Finally, in many communities, the local building department will usually be more than willing to answer questions about zoning and building requirements and may in fact have a set of plans that can be copied. Richard Berry

Thanks - this is great advice!

Vicki,
Taking the conversation in a different direction. If you live in the Chapel Hill area, give Eric White a call. He is a real estate agent and has very good contacts for building projects. Mention my name...he has been assisting me with the possible relocation to that area. Eric White: Eric@iamChapelHill.com or my cell number 919-360-2935.