If your lot is in California's Contra Costa County, then this procedure will work for you.
You will need:
1) A modern web browser (I like Chrome http://chrome.google.com)
2) A PDF viewer (preferably one with a browser plugin like adobe reader)
3) Your assessor's parcel number. This is a 9 digit number that is used to identify your lot, it will appear on your property tax mailings, etc. (for the purpose of this demonstration I will be using a lot in Lafayette that is currently a part of Briones regional park APN:231080003)
The specific GIS site we will be using is located here: http://gismap.ccmap.us/imf/imf.jsp?site=ccmap
Step 1: Step 1: Locating the Lot
Once everything loads after a few seconds, you'll want to click "Locate Parcel by APN" on the right-hand panel. After you do this, enter your 9 digit Assessor's Parcel Number ( I'll use 231080003 ) then click "Submit" It will take a few seconds to find your Lot.
Step 2: Step 2: Adding GIS Data Layers and Scaling the Map
On this page you can do lots of neat stuff including view some public records about this lot, and even see property tax information. You can also export a list of mailing addresses for the neighboring lots. (based on the address of record for the deed) However, we wont worry about these features for this instructable, our goal is to produce a scaled site plan.
To Proceed, click the Layers Tab in the upper-left corner.
Now, you'll be able to view a list of available GIS data layers on the right-hand panel. You can expand and collape groups of layers, and check and un-check layers to customize your map.
You can zoom and pan the map view with the map controls. (They work a lot like google maps)
After you've selected your layers, and got the view that you like, you should adjust the scale to something standard. The scale is in the bottom left corner of the screen. (your view will change as you adjust this number) When choosing a scale its important to pick a value that architects, engineers and contractors will be able to use. (I suggest you use one of the ones commonly found on architect's and engineer's scales like this one: http://www.amazon.com/Staedtler-R-Architects-Printed-Scale/dp/B00006IAOW/ref=sr_1_3?ie=UTF8&qid=1377543157&sr=8-3&keywords=architect+scale)
These are found on common architectural scales, and will only be suitable for small to medium sized lots:
3/32 inch -> 128
1/8 inch -> 96
3/16 inch -> 64
1/4 inch -> 48
3/8 inch -> 32
1/2 inch -> 24
3/4 inch -> 16
1 inch -> 12
These are found on some engineers scales and will probably be the most useful for large lots:
1/100 inch -> 1200
1/200 inch -> 2400
*Note that further zooming will affect the scale you've set.*
Once everything is set up, click the "Print Map" button in the top-right of the screen, and proceed to the next step.
Step 3: Step 3: Exporting and Printing the Map
-Select the paper size and orientation ( I chose 11x17 Landscape)
-Use the current Scale
-Enter a name for your printed map. (This will appear as the title on the printed page)
Now, click "Ok". You will have to wait a few moments as your PDF is generated.
When it's finished, the right hand panel should change and display a link to your PDF. (second image) click that link to view the PDF in your browser (or download it, depending on your browser's settings)
There is your finished map! Download it and print it like you would a normal PDF. The scale will only be valid if you print on the same kind of paper that you chose in the print setup form. Be sure to print with 1:1 scaling in your PDF viewer's print settings page.
I've attached the PDF generated by this procedure.