These days it seems you can get free (as in free beer) software for just about anything, really. Drawing diagrams is not exception. I've used the free Inkscape software (
I ended up hiring the same engineering company that designed the development I live in and for $150 they came out, re-marked the corners of the property and supplied me with a printout and the DWG file of the property. In other words, there is no good reason to pay for software to draw it, it's available for free. However, you probably still need a professional with the specialized equipment to take accurate measurements for the drawing. In my case, I'm sure they didn't need to draw the property from scratch and just cut out my little part of the complete development plan from the construction documentation. Perhaps you can find some of the pre-existing drawings of your property, too. Otherwise an engineering company will be well equipped to both measure the property and create a CAD drawing which you then should be able to import into a number of free programs, such as Inkscape I mentioned, to make any additions and alterations you need for the project at hand.