JOURNAL STAFF SIOUX CENTER, Iowa — Construction starts soon on a $8 million indoor sports complex in Sioux Center that officials estimate will attract 200,000 visitors per year to the city of about 8,200. The air-inflated dome, a joint project between the city and Dordt University, will host youth and college sports teams, adult athletic and wellness programs and tournaments. The turf will be designed for soccer, youth football, softball, athletic practices, recreation activities, and other multi-purpose uses. The structure will measure 250 by 470 feet with a height of 75 feet. The main entrance will be an 8,400-square-foot building, which will house offices, restrooms, storage, concessions and seating for…