Start by reading where water already goes: the natural flow paths, the low spots, the culverts up and downstream. Then design the pad and grading so water moves around the structure, not against it, with swales, culverts sized for the crossing, and finished grade falling away from every wall.
More detail
Drainage planning is done standing on the land, preferably imagining it in a February storm. The first read is the existing water: which way the site falls, where sheet flow concentrates, what the creek or bar ditch at the boundary does when it rains hard, and whether any part of the site sits in mapped floodplain, because county floodplain rules apply even on unincorporated land where nothing else is permitted. On the Blackland side of the corridor this read matters double, because saturated clay effectively stops absorbing and everything that falls becomes surface flow within minutes; on the sandy west side the failure mode flips to erosion, water cutting channels through loose ground. The design then works from the structure outward. The pad rides high, with finished grade falling away from every wall (roughly 6 inches in the first 10 feet is the working residential rule) and roof water discharged well away from the foundation, not at the drip line. Swales and bar ditches intercept and carry flow around the pad instead of letting it arrive. Culverts get sized for the water that actually crosses (the county road department has opinions where their road is involved), because an undersized culvert is a future washout with a schedule. Driveways cross the drainage plan rather than dam it. Doing this before the dirt work costs a site visit; retrofitting it after a slab is down costs a different order of magnitude, which is why every pad scope here carries the drainage plan inside it.