Old technology , About 15 years ago, I built on an extension to the garage for a workshop. To layout the right angles, all I used was a tape measure. Using the 3,4,5 proportions to an isosceles triangle. For elevations I used a water level, some clear sections of plastic hose attached to a long section of garden hose. One end mounted to the original garage, the other mounted to a stick length calibrated to the top of foundation. Just move it a round to set the form height to match.
The neighbor guy was a surveyor and checked over my layout and said he couldn't have done any better with his transit. I had seen the local Amish builders do it this way and thought I'd give it a go.