Project Bidding Web App in PHP/MySQL/HTML5/CSS

We are looking to build a similar website to mybuilder.com, which is a website where users post their job or project to be completed and builders bid on the project to try and win the user's job/project.

ARCHITECTURE
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* We would like 3 tier architecture and ideally MVC architecture
* The architecture should allow for an unlimited number of child websites to be created under the same parent code base with localised settings. For example, mybuilderspain.com and mybuilderusa.com may be child websites running off the same parent code at mybuilder.com.

DEVELOPMENT
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* We would like the controller and database layer of the website to be built in a PHP and MySQL framework and we would like the presentation layer to be built in HTML5, CSS3, JavaScript and JQuery
* We would like a mobile and tablet friendly CSS style sheet
* We may consider a native mobile application developed for iPhone and Android through PhoneGap or Appcelerator

SCALABILITY
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* The website should be able to handle 50,000 users a month

TESTING
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* There needs to be comprehensive unit testing for all the code
* With regards to website cross-browser testing we would like testing to be completed for IE6, IE7, IE8, IE9 and the latest versions of Chrome, Safari, Firefox and Opera
* With regards to the mobile website there needs to be testing performed for iPhone, iPad and Android

BACK OFFICE FUNCTIONALITY
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In terms of back office we would like the following back office functionality:
- Basic Site Stats regarding users
- User management
- Content management
- Ability to add an unlimited amount of SEO Rich landing pages through the back office
- Category and Sub Category setup
- Region and City Setup
- Notification Email management via SMTP
- Admin tools
- Payment processor setup (PayPal payments integration)

SECURITY
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- Major security considerations (malicious code execution etc) and guard against database & website hacking

SCOPE
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With regards to scope we would need some flexibility in terms of increase or changes in functionality, however as part of our designs we will provide the following documents so there may only be small changes because we have already produced the majority of the design documents including:

A semi working prototype of the final design
List of all the fields and options to be used in the website including a City Listing, Category and Sub Category Matrix
Email number, contents and format
List of all error messages and error handling
List of SEO requirements for the SEO landing pages

WHO ARE WE LOOKING FOR
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This project is open to companies where there is a small team of developers who have worked on similar projects of equal complexity. We would like to see:

- Previous examples/portfolio of work that you have created
- What your recommendations are for the exact technologies and frameworks to use in this project
- An estimate of time / cost of completion
- The number of dedicated team members to this project and what their roles may be

REPORTING, PAYMENT & PROJECT PLAN
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* We would like to see a project plan which details the agreed milestones for the project together with the details of stage payments due at the completion of various milestones
* We would like a way of reporting and tracking bug and defect requests

NON-DISCLOSURE AGREEMENT
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We will release full details of all the documents after the chosen developers have signed a non-disclosure agreement.