You will need to share with up your skill set if you want an answer but usually you need an architect to plan an addition that does not look like an addition when done and they usaully have a structural engineer on staff.

Hire an architect to design the addition and produce construction documents. Share with the architect your wants and needs and budget. Hire a builder during the design process to estimate costs and build the addition in accord with the construction drawings. If the design requires a structural engineer they can be hired during the design process. Good luck with your project.

Perfect thanks Mark!