As an scorp, we purchased a building as our main location. How do I handle this tax wise. Do I deduct the mortgage payment the same way I used to deduct my office rent payment? What about the 30% downpayment I made. How do I handle that? Thanks in advance for any help.
No. You add it as an Asset and depreciate the cost over years. That will take care of the purchase price (including the down payment). You can deduct the interest part of the mortgage.
Ok ... the payment is NOT a deduction on the return ... however the interest you pay is an deducible expense and the purchase price of the property MUST be depreciated per the IRS rules.
I highly recommend you seek local professional assistance to understand basic bookkeeping concepts and how to file the corporate return (which is due 3-15) and the required quarterly fed/state payroll tax forms.
Does the S corporation actually own the building? If that is the case, it is usually not the optimal method (as opposed to a separate entity (or individual(s)) owning the property and leasing it to the corporation).
As @Critter-3 mentioned, you need to seek local professional assistance as soon as possible.