For 100% daylighting from traditional skylights, approximately 5% of the roof area should be skylights. However, the benefits of daylighting must be weighed against the unwanted effects of heat gain/loss through the skylights.
The skylight specifications depend on climate. In all climates, use skylights with a high visible light transmittance (Tvis or VLT). Hot climates should have a low Solar Heat Gain Coefficient (SHGC). Cooler climates should have low U-value. Tubular skylights require a lower skylight-to-roof ratio (SRR) than traditional skylights, approximately 1-2%.