How do you determine (approximately) how much something like an extra bedroom or bathroom is worth, or extra square footage or a larger lawn?

Hi everyone,I'm cold calling owners in my area, San Francisco and the Peninsula, and I'm targeting vacant lots or properties with enough square footage to build small multifamily, luxury SFR, or luxury condos on them. 

I am not sure how to phrase this question, the county record for a rental I am selling is incorrect, it does not have the correct square footage for a permitted addition, and the number of bedrooms is listed as three instead of four.

@Jon Sirkin Assuming all are comparable in square footage and location, be careful how quickly you raise the rent. 

And indeed, it has always been as simple as writing a single letter.Sounds like Kel will be posting a sample letter to help others but the key thing I do to make my case is to find the *cheapest* 3-5 houses that sold near me and then compare their selling price/sqft. to my square footage.

The square footage of the suite is 280. 

But I do have multiple matching square footage, bed/bath, and have had repair work done.  

All properties are similar square footage and 3-1 and 3-2.I've been breaking them apart and trying to compare as J Scott recommends in his "Book on Flipping Houses," and we still can't determine exactly where the property falls.Does anyone have any advice to sort through all the data regarding comps?

Most Security systems only maintain footage for 2 weeks dueto camera memory capacity.I.

Most Security systems only maintain footage for 2 weeks due to camera memory capacity.I.