Above shows a two-car garage addition to an existing garage. I moved the new two-car garage, on the left, back a few feet to blend it better with the home and allow natural light through an existing window into the original two-car garage on the right.
Always try to get three bids on everything. You can learn a lot from the bids- its not just the price.
Be sure that you and your contractor follow a change-order policy for any changes. This means that you and your contractor sign an agreement describing the change and agreeing to the cost before the work on the change is started.
If you want to buy all the materials on your credit card for flyer miles, run that by your contractor as part of the original construction agreement.
Painting the interior and exterior is an easy sweat-equity option for anyone trying to hold the cost down.
Tiled entryways or bathroom floors can get cold in the winter. Look into electrically heated mats that are placed below the tile and are attached to a thermostat.
During construction check on the grade stamp of the framing members. You should see #2 or better but if you find a #4 grade that is bad news. The grade of #4 is considered utility grade and should never be used for framing.
If you determine that part of your structure is too close to a lot line, you can request a variance with the local planning and zoning commission. Usually you have to demonstrate a hardship that the new addition would eleviate.
Be aware that you may need an asbestos test done in an existing structure. You will probably need a soils test for any addition and an engineered foundation plus a survey showing the distance to the lot line of any addition.
If you have questions, email or text me.