Ok, this will do it for you.
Los Angeles County Assessor's Office - Property Assessment Information System
Accept their terms, and enter address then click on assessor's map and you have property line and dimensions. Your architect can go from there. He should know how to get that in his sleep. If you are looking for the plot /site plan then its in the city or county depending on your location. why are you looking up this info? That's the Architect's job to local the site plan. He should be able to get that in 10-20 minutes down at the city.