Small ships do not cut it in the void. Most ships large enough to include a stardrive economically are over a kilometer long; anything smaller is generally unable to contain enough mass to be worth moving between stars, whether that mass is cargo, manpower, or firepower. The smallest common model of ship equipped with a stardrive is the Nawarat Shipmasons’ Grey Goose fast courier, a mere sixty meters long and 7.5 tall.
While most small vessels – shuttles, gunboats, bombers, cutters, pinnaces, yachts, dropships, etc. – are small enough that building them out of processed metal is an affordable option, any ship of significant size would require enough metal to depress a country’s (or even a planet’s) economy for the several years it takes to build the ship. The solution to this problem, as shown by the fraal to the humans and discovered independently by the t’sa, is to create starships out of stone. Shipmasons, surveyors, architects, engineers, and miners spend months or years creating blueprints and plans, then hollowing out asteroids to accommodate the hardware and personnel required to make a space rock hundreds of meters long into a starship.
This doesn’t mean that starships all look like dried, pockmarked potatoes, though. Each ship is as carefully and painstakingly carved from its parent asteroid as any artist has carved a marble statue. A single misplaced blast or unnoticed seam of softer rock can compromise months of work, risking turning out an inferior superstructure with a fatal hull breach just waiting to happen. Aesthetics are not ignored either; after all, no one wants to invest millions or billions of currency units and thousands of man-years into a ship and have it come out ugly. The outer hull of the ship is generally buffed smooth as any metal-skinned ship can hope to be, often heat-treated and polished to be as smooth and slick as glass. Larger ships are more likely to be built to custom plans than generic blueprints, and thus often come with more baroquely-carved hulls – ships owned by the human religious sect the Jesuits all have large statues of Catholic saints carved into the prow, for instance, and the Hegemon’s throne-ship is carved to resemble a walled city.