I have to concur with the others who say don't. Having always fallen strongly into the "don't reinvent the wheel" camp, I spent a number of years analysis various CRM offerings (Sugar, Zoho, Dynamics, etc) for our own financial services business needs. I finally settled on Dynamics and hindsight has proven it to be a wise decision.
In 2 years, on a shoestring budget, with an outsourced dev team, we've been able to build a vertical solution (soon to be released) that blows away the incumbent software offerings. The key reason is they are all founded on an in-house, limited CRM system that simply can't compete with the capabilities of Dynamics/Salesforce/etc. When you combine the capabilities of Dynamics with its ever-improving integration with Office 365 + Power BI, there's simply no point trying to build a CRM from scratch. Focus your time/money on the value add layers that sit on top. You'll get to market more quickly and your customers will have a more capable system.
My 2 cents (before currency conversion) :)