Design rain water drainage for warehouse layout

Overview of the project - We have warehouses built over a rectangular land 561 ft x 103 ft. Currently there is some very basic drainage. We are located in the region which receives heavy rainful during monsoons. At times the rainwater from the outside drainage flows back to our layout and risking entering inside few low lying warehouses. So we need to ensure that the rainwater in the layout is drained out and we need to avoid any back flows. I have couple of ideas on how to design a solution which is cost effective as well as effective. I would need expert's advise on the design so that I can do it first time right. P.S - This design is just for rain water and not for sewage water. 1. Annual rainfall in this region is 2810 mm. Assuming 60 days of rainfall in an year, the daily rainfall is around ~5 cm. So the amount of water that needs to be drained out every 24 hours is 275k litres. 2. The layout is approx 58k sq ft and has shed on around 40k sq ft. So around 69% of the area is shedded and 31% area is open to sky. 3. One option I am exploring is to make running gutter along the roof and route along the shed wall towards the outside drain. This will help shed 69%(190k) of the rain water. 4. For the rest of the rain water ( 85k litres ), I am planning to build hollow chambers of dimension 2ft x 2ft and sloping depth every 75/100 ft to route the water along the ground using 6 inch pipe to a sump near the outside drain. From the sump we need to either use a sewage pump or slope to drain the water to the outside drain. The ground will be levelled to ensure water flows into these hollow chambers. 5. The two open areas are not connected and so we might have to build two sumps. Each sump then has to discharge ~ 42k litres of water. I have a 0.75 KW sewage pump which can discharge around 200 Litres per minute. So it will take 3.5 hrs and cost around 0.5 $ to discharge the water daily for one pump. ( 0.1 $ is the electric charge per 1 KWh). Both pumps operating cost would be 1 $ per day which is quite reasonable. Objective of the project. 1. Need to identify design of sump, under ground chambers, pipe dimension, sloping, placement of sump. 2. Reduce overall cost of the project. ( By reducing number of chambers, pipe usage, sump, electric usage etc) 3. Design of the sump so that we can use gravity / pressure to discharge water and need not use sewage pump ( Can we have the underground sump top end slightly intruding at the top) 4. I do not need very detailed CAD / CAM design. Some basic representation should be fine. 5. Do I need to care about 31% water at all and let the ground absorb the water. 6. Overall cost for this assignment should be less than 150 USD.