Is the code required concrete pad at the outdoor installation point.Is it a ground, roof or cantilever type outdoor installation.Is the equipment all the same brand and size for all of the bids, or is it Carrier vs Goodman, etc..X tons vs Y tons.Are they all including coolant gas in the bid (the new stuff is astronomical in price).Are they including new copper lines in the bids, or just the inside and outside components in some bids.What I'm getting at above is are the bids apples to apples....It the whole Air Conditioning system magic to you--like pulling a rabbit out of a hat, and you are a fish out of water about how it works and it's parts and terminology?

Hi,I plan to buy 1.5 acres of pad site in a commercial property that is being setup.

Add in 5% vacancy and your down to a $1500 net (still not pad on a $20,000 investment, but 7.5% ROI is just average.   

It's the natural grade at the house corners, possibly the AC pad or other lowest equipment servicing the residence, deck or porch attached to house, garage slab elevation, basement floor, crawlspace.

@Concetta ParsonsIf your metal roof is noisy it was either installed incorrectly or long ago before they put pads or rigid insulation down before the roofing.  

It wasn't straight on the carpet, but through the carpet and pad.

When the l/o failed (partly) because the sprinkler system twice flooded my full, finished basement @$1800 in carpet and pad, drying it myself each time. 

Something will put the brakes on the madness.

When someone's mother (or father) falls when at your facility relatives are going to ask you what you did not do to prevent their mother from braking her back.

Anyways, good luck to you man, and ALWAYS pad your number for unforeseen expenses.