This paper reports the productivity of a small-scale pilot biofarm of grey oyster mushroom (Pleurotus sajor-caju (Fr.) Sing.). The pilot was tested in Mekelle city (Ethiopia) in a brick-walled dark room. Growing structures were constructed by erecting three wood poles and fixing them with three wooden side bars at multiple locations to make a prism-shaped rack with multiple triangular open shelves, each capable of carrying one bag of spawned substrate. Mushroom substrates were prepared from maize stalk and wheat bran supplement. Pasteurized chopped maize stalk and wheat bran were mixed at the ratio of 10:0, 9:1, 8:2, and 7:3—yielding four treatments. Five kilograms of substrate was taken from each treatment and was mixed with one kilogram of gypsum to produce a growing mass. Each mass was spawned with 200 g of inoculum under aseptic conditions and put in polyethylene bags. The treatments were replicated thrice and the bags were put on the growth racks in completely randomized design. The growing room was maintained at optimum conditions. Maize stalk substrates supplemented with 10% and 20% of wheat bran have resulted in statistically comparable productivities but statistically significantly higher than those grown on nonsupplemented and highly supplemented maize stalk substrates (p ≤ 0.05). The ingenuity of the design and the convenience of the construction of the racks, the availability of the substrates, and the simplicity of the management and maintenance of the biofarm rendered the piloted design suitable for home-based and small- and medium-scale mushroom biofarm entrepreneurship.