Looking for an ERP for an elevator company.

I have been assigned to create an ERP for a company which manufactures, installs and services elevators.

They are looking to build the ERP starting from sales, design, production, inventory, despatch, installation and commisioning followed by their service support consisting AMC and breakdown calls.

Also which do you think will suit the requirement? A custom made software or a software which is readymade like odoo/katana? Maintenace cost is a constraint as they do no want to spend much year on year. Also what will be the timeframe to implement the same.

Kindly help me to recommend them a perfect solution.