I don't quite understand. In the interior photo the window looks like those on the second story, above the garages. Will you be building at that level? You said 780 sq ft, but what are the expected exterior dimensions. The 20 by 20 BR you mentioned isn't so very large, especially if you include the closet sq footage in that. That would still leave office and bath sizes of 12 x 12 and a pantry near 100 sq ft. Hallways can eat up a lot of valuable space, so knowing the exterior dimensions is important.

Work with a local architect, that is the kind of work they do.

Outside will be 30x26! I was thinking bedroom dimensions without the closet and we have a split foyer so the living area will be above the new garage

Why will it be 30x26?

A200K+ project like that requires the use of a local professional. Find one.

The driveway area is that size. My husband is a contractor and will do the building. We are in the primitive stages so im just trying to get an idea of layout to give an architect a more concrete idea of what we want

Why don't you get some graph paper and sketch several plans? If your husband ever has customers or workers come to his office you might want an exterior entry, and that might influence the placement of the office. Also, consider how far removed from the kitchen your pantry will be and whether you need to be able to hear young children in the other bedrooms from the master. Without those details, plans from others aren't likely to be of value.

Tell the architect why you want to add onto your house. Answer their questions, then in a few days they will show you how big it will be.

You have a problem and the architect will have a solution. If you give the architect a solution they may have a problem. Architects turn people's needs into architecture, the site and your needs determine the size and configuration.

Designing add on spaces is not as easy as it appears. Actually the smaller the 'new space' the more difficult it can be to design something that flows with the rest of the home without looking like an add-on space. As a long time Realtor, I have shown homes with additions that look natural and others that have a severe degree of functional obsolesce. Functional obsolesce will reduce the value of your home many more times than the cost of an architect. Getting a good design from a good architect actually creates value much more than the cost of the architect. I don't say this lightly. Add on spaces are very prone to the old adage: You don't know what you don't know.

PS: You don't need to supply a plan to an actual architect. If your space plan designer wants you to provide him/her a plan before they will start work, then they aren't an architect.