Assuming SpaceX hits their 100T to orbit goal, one relatively full load of steel plates at 6.36m² x 0.31cm thickness (and roughly 175,000 lbs) laid out in a square would be a flat surface of 484m². If you think about making a bigger ship where the surfaces are 484m², you can build a borg (https://en.wikipedia.org/wiki/Borg) cube style vehicle hull in a month… or a drake cat hull ( https://starcitizen.tools/Caterpillar) style vehicle of 5325m length in less than a year (assuming they can match current capabilities of weekly launches and not the multiple times daily that SpaceX has ambitions for).
As a visual reference: 484m² is roughly 210 shipping containers square and 5325m is roughly 978 shipping containers long. This type of vehicle could easily self-sustainably support a crew of 100+ very comfortably with current o2 tech. SpaceX and others will no doubt improve on and significantly advance the life support tech needed for larger sustainable space vehicles.
As with most estimates, all these numbers have rounding slippage at every level of the calculation, but this is actually a good thing given that the vehicle hauling things to orbit (Starship) is currently in prototype form and having extra wiggle room on volume and weight is a good thing.