Level 1 and 2 will have one Cisco 3750 switch.
Level 3 will have one Cisco 3750 switch.
Level 4 will have one Cisco 3750 switch.
Same applies for Building 2.
There will be two core switches Cisco 3750. Each core switch will connect to every level switch in building 1 and building 2. In case one core switch fails, the users in both buildings would still have their traffic passing through other core switch. Both the core switches should connect to Cisco ASA and then to a primary router that could be Cisco 3825 and a backup router. Both routers will connect to two different ISPs one serving the purpose of primary and other as backup. The capacity of primary for 90-100 users could be 6-8 Mbps and backup should be 3-4 Mbps. Both the routers will have BGP configured with respective ISPs, and EIGRP with Core switches. Each switch in building can have default gateway set to Core switch or on the other hand same EIGRP could be configured.