The start of the real construction of your home, barn or whatever building.
99 out of 100 times you will have to dig into the ground to place the footings of your foundation. Hire an excavator who has the right sized equipment for the job. Hiring a too small excavator with a low hourly rate could end up costing you much more in the long run.
You will need to excavate an area based on your building size and where it has to be located on your property as per zoning bylaws. When you are digging you should always over excavate the hole to make sure you can easily work around the foundation. Quite often you will have to install a perimeter drain and you will need room to do that too. Much cheaper doing it right the first time, than having a machine come back afterward.
To get the hole in the right place you need to locate the corners of your building and extend outward from there. Depending on the height of the foundation, 3' diagonally would be the minimum.
Trenching or Excavating the Whole Area
For certain situations, you could instead of excavating the whole area, dig trenches where your footings are located. This will work great for simple layouts. But if there is plumbing located under the slab you could create a lot more work for a plumber. Excavating the whole area nice and level, stepped if needed, makes the work of building your foundation much easier. So suck it up and don't get cheap too on the excavation.
Piling the Dirt kept Onsite
Start off with removing the layer of topsoil, that is, if there is any. Place this in a separate pile out of the way and try to keep it uncontaminated from other materials.
You usually end up keeping some or all of the excavated material onsite. Keep the better material, and I know it all takes time, sorted into material that would be nice to use inside the foundation and a pile of material that can be used for backfilling the outside.
Pile the excavated material all the way around the hole for faster digging. Or not! That has to be one of the dumbest things you can do when excavating. Most likely you will need to use at least one of the rear and front corner pins to get your setbacks. Keeping one side clean makes a whole lot of sense! Keep an area in front clean too, much easier to get to the hole.
And also consider while having a larger excavator on site, digging the area where the sewer has to go. The connections for sewer and water line are usually deeper in the ground and it would not hurt to do your other services connection at the same time. If there is a gas line going to the house, don't worry about digging that out. The gas company will take care of that after the final grading of your lot. Note the exact locations of any service lines you install on your plot plan and follow the motto, locate before you dig!
Consider getting your surveyor to come to the site 3 times. One time to locate and mark the corners for the excavation. A second time to locate and mark all the required corners for your foundation and a third time for the official survey certificate. I will cost you a wee bit more but you will sleep much better!