Need an developer for B2BC platform

We are looking for an experienced full-stack development team to build a modern, scalable construction management platform from the ground up. The platform will serve multiple companies (multi-tenant SaaS) and provide role-based access for business owners, administrators, sales teams, production managers, field workers, and customers through web and mobile applications. The project includes: Main Web Application Admin Portal Cross-platform Mobile Application Shared backend API and database Modern UI/UX with responsive design Secure authentication and role-based permissions The platform combines CRM, project management, workforce management, customer portal, calculators & estimation tools, document management, accounting workflows, communication features, subscription billing, and business operations into a single ecosystem. We already have a detailed functional specification describing every module and workflow. This document is attached to the job post and should be used for estimation. What we're looking for Senior full-stack development team (not beginners) Strong experience building complex SaaS platforms Experience with scalable backend architecture React / Next.js expertise for web React Native (or Flutter) experience for mobile Experience with cloud infrastructure and API-first architecture Strong UI/UX implementation skills Good communication and ability to work with milestones Your proposal should include Please provide: 1.Estimated timeline 2. Development cost Please review the attached specification before preparing your estimate, as it contains the complete lis