When selecting the physical location of the tower/mast, there are a set of things that you should bear in mind. Naturally, you must make sure that you have the necessary free space on the ground where the tower will be placed. Check the specifications of the tower/mast that you aim to purchase for the size of the footprint.
The ideal site for a tower/mast is a flat, level field. However, any reasonably level space, in which there is sufficient space for the base foundations, can be utilized. The site should be free from obstructions like trees and buildings. Not only the spot for the tower needs to be clear, also the surrounding area as you will need some free space when assembling the tower.
Do not forget that trees have roots. Digging a hole through a massive root system is not a dream.
Medium sized and tall towers/masts normally require massive digging since concrete foundations must be put in place. Always call for underground utilities check to make sure that there is no infrastructure dough down at the place you have planned for your tower/mast.
Also, if the tower is high, always check with the regulators in the country if you need to apply for a license and/or register the tower to any authority. If the site is close to an airport, there are special regulations that need to be followed.