Build a Custom Construction Management System

We are a General Contractor looking to build our own internal web-based construction management software — a simpler version of Procore that we fully own and can host ourselves. Core Features Needed: Employee login system Client and Project tracking with automatic job numbering Contract management (both Owner contracts and Subcontractor contracts) Change Orders Invoicing and payment tracking Document management with Google Drive integration Labor compliance and sick leave tracking The system should be built in a way that we can easily add new modules later, including giving login access to subcontractors so they can upload invoices and documents. Please reply with your experience building similar systems and your estimated timeline and budget.