first, my church is a two story building and we use the gym to worship in on sundays. its like a school, i guess, with classrooms.
as for money to build: well those big glass and fancy places have hundreds and hundreds of people who tithe and fund-raise for years to build. my church is much smaller. we all donated over several years and did things in stages (planning, blueprints etc) and did a lot of the work to actually build our building after meeting in a real school for many years. no millionaire donors but plenty of little guys that supported the project.