Purpose: To evaluate the effect of build angle on the flexural strength (FS), elastic modulus (E), and hardness (VH) of stereolithography (SLA)–based 3D-printed custom tray resin. Materials and Methods: 3D-printed specimens with dimensions of 65.0 × 10.0 × 3.3 mm ± 0.2 mm were manufactured with different build angles (90, 120, 135, 150, 180 degrees) using custom tray resin. For preparing the specimens in the control groups, the autopolymerizing (AP) resin and the ultraviolet polymerizing (UV) resin were used. FS and E were determined by a three-point bending test, and hardness was evaluated with the VH test. Fracture surfaces were evaluated with scanning electron microscopy (SEM). Statistical analysis of the data was made using one way ANOVA followed by Dunnett T3 test. Results: Considering all parameters, the UV group was statistically significantly lower than the other groups. The mean E value of the 90D group was statistically significantly different than those of the 150D group (P = .000) and the 180D group (P = .002). The mean E value of the 120D group was statistically significantly different than those of the 150D group (P = .003) and the 180D group (P = .013). The AP group showed a higher mean VH number (20.20 ± 2.08), and the difference was statistically significant compared to the 3D-printed groups (P < .005). Conclusions: Considering its mechanical properties, it was appropriate to arrange the build angles at different degrees when manufacturing reliable custom trays using SLA. The 3D-printed custom tray production method was a more standard method compared to AP and UV.