Aggie Stadium So I have spent the past few years project managing stadium/arena construction and renovation for a multi-facility owner. (Anyone in Athletics feel free to PM me if you wish). I did a brief count, and there are about 8800 fixed seats, which means they figure about 1000 per endzone. Measuring, they are allocating about 15sqft per person on the grass, which is typical for a "non concentrated occupancy". I don't know Davis code, but nationally, you provide 0.2" of exit width per occupant. I count 18 pedestrian gates, call em 10' wide and we're right on the money.
To expand Aggie Stadium, the seats are the cheap part. The money gets tied up in supporting infrastructure IF that is not already in place, as well as administrative construction soft costs. For example, in my jurisdiction, I have to keep a ratio of 1 toilet per 90 seats which is supposed to ensure a wait time of less than 3 minutes. Let's just say that's what the building department at UCD uses, that would mean AS has about 120 toilets. Even simple restrooms are more expensive than you think. Now, hopefully the planners recognized this as a possibility and upsized the utility loops in the stadium. Costs very little at initial construction but gets very expensive to redo later.
Now, what expansion would make the most sense? Until we routinely break 10,000, the only thing that makes sense is to negotiate a standing room oversell with the fire marshal and bring in portolets if the math requires. For a permanent structure I would say a second deck on the Aggie Pack side if you could commit to mostly 7pm games. Cantilevered over the AP would be expensive, but a steel superstructure over the walkway and restroom buildings with aluminum bleachers would be economical. In fact you can see the gaps in the restroom buildings are spaced right for stairways going up. Lets say you did 20yd to 20yd, so 5 sections or roughly 2300 seats if its the same size sections as existing. You'd probably get the same net gain filling in the end zones, but in the process take away a popular family hillside and replace it with poor sightline seats that aren't going to command much premium - unless you move the AP to north end zone like Toomey. That was a lot of fun down there. But back to brass tacks, all that concrete is going to cost you more than a steel structure. That kind of poured in place concrete is a lot of material and labor intensive... gotta get it graded, stabilized, concrete trucks there, formed up, finishers working and everything measured right in the field. Off by an inch? Get the jackhammers. With an engineered steel structure it all comes precut from the factory with less opportunity for expensive field screw ups.
As to the comment about the cost of steel, that's probably not what broke the budget on Aggie Stadium. In real life, they built it at a construction peak - shortage of workers and supplies in a boom drives general contractor prices, kind of like right now. If they had waited to build it in the recession, you would have found bricklayers and plumbers working at a discount. Also oil prices were spiking, which had to have influenced the cost of the massive earthmoving effort to dig that bowl and then truck in all that concrete. Throw in a wet winter and the GC was able to justify his underbid - note that up to that point the contractor had mainly only built apartment buildings. Looking at comparables, you probably could have done a 20,000 seat (plain but functional) surface stadium with a qualified contractor for the price we paid.
Ok, end of the novel. I could talk at length on this, so let me know if you want more.