What do they look for when they assess my home?

They will look at lot size, square footage of home and general condition, average, poor, good, etc. This will become a permant record, so "poor" is bad for resale, but better for your taxes.

Only legal rooms count, the basement will not come into play at all. The rooms that are legal will be counted and living space (not basement) measured.

They'll look at the general condition, size, number of bedrooms/ bathrooms; etc. If I were you I'd walk around with them and talk down your place, discussing all the problems you have told us (roof leaks, basement flood, etc). Its just human nature that this may affect their view of the lace a bit. What would also be great is if you could get a realtor to run off the comparable listings to your house that have sold recently, or even do a CMA (comparative market analysis) of the place. If this data shows that places similiar to yours are selling for less you should show this to the assessor and tell him how your place isn't really worth so much.

Anyhow, best luck. Bear in mind that many areas are desperate for revenue as dropping prices are cutting their income so much that many counties/ towns are really suffering. So, they want to get any revenue they can, but that doesn't mean they can overcharge you on the taxes you pay.

There are many methods available to counties in how complex an approach they take to ad valorem (tax) appraising.

Land value and dwelling value form the base. Imagination seems to be the only limit after that.

A nearby county in my area assesses brick mailboxes, concrete pads under air conditioner units, dog runs, finished and unfinished basement space, and almost anything else on the property that can't be easily moved. They also grade the perceived quality/condition of the house at one of five levels.

The best way to find out is to ask. Call your county tax assessor and request a copy of the assessor card for your parcel, it's generally a public document. Many counties have their records online, others may have a public access computer in the assessor's office.

County property tax assessors??? They look for the recent sales price in the area. They don't add or subtract for good or poor property condition.

Property Appraisers for mortgage loan purposes? They look for the recent sales prices also, but they do subtract for the need fixing items if it's a huge item. Below ground living space is not counted, finished or unfinished. The roof is a major item. Depending on the loan, they my do a full appraisal, looking inside and outside or just a drive by, looking at the outside only.