Is it possible to build Data warehouse by myself?
It's a lot like asking, "Can I build a house by myself?"

It depends a lot on what your definition of "house" is. Talk with your internal users to build a set of requirements first - that's going to need to happen regardless of who builds it.

When you're done building requirements, then you can start sketching out what you'll need to build in order to satisfy those requirements.

Then, you can start building time estimates for what needs to be built.

As you work through this process, you'll have a better understanding of what the house looks like and whether you can build it yourself with your existing toolbox and skills.