A metal shop or barn is the best value in construction per square foot, which is why so many properties around Alvin, Rosharon and Angleton have one. It's also the project most likely to go sideways, and almost always for the same reason: the shell arrives before the site work and the paperwork are settled.
Start with setbacks and permits. Requirements differ between city limits, county jurisdiction and whatever deed restrictions came with the property, and they govern how close to a property line the building can sit, how tall it can be, and sometimes what it can be used for. This is a phone call and a site check, not a guess, and it needs to happen before steel is ordered because a building sized to the wrong setback is a very expensive stack of panels.
Then the slab, which is where most of the real money and all of the longevity live. Drainage first: on flat coastal ground, a pad that sits level with the surrounding dirt will take water in the first serious rain. The pad gets built up, compacted, and the slab poured with the reinforcement and thickness the building and its contents actually call for. A shop that will hold a lift needs a different pour than one holding a lawn tractor.
Sizing is the part people most often regret. The rule of thumb worth following is to figure out what you intend to keep in it, then add a bay. Height matters as much as footprint: eave height determines whether a roll-up door can clear a trailer or a truck with a rack, and raising it later is not a modification, it's a rebuild.
Finally, decide up front how finished you want it. Insulation, wiring, lighting, a slop sink, a framed-out office corner. All of it is dramatically cheaper to install while the frame is open than to retrofit after the panels are on, and it's worth pricing as a separate line in the estimate even if you defer it.