Building a duplex house plan is a good way to start small in multifamily housing. The blog Guide to Finding Your Duplex House Plans is helpful in selecting your construction plans. http://www.houseplans.pro/blog/post/finding-right-duplex-house-plan

Whew! So much to say, so little to go on. First...you need an architect. Hire one. Then you need an engineer. Hire one of them too. Hiring a contractor to consult on cost and practical issues is a good thing too. Once your team is assembled, listen...hard! Best of luck!

One of the first issues is the orientation of the house. Solar panels do better on the south side. You should research whether your roof needs to support more weight. You will also do well to consider all aspects of solar building --- you can find books available in e-format for this. Go to Amazon and read reviews carefully. Things like roof overhang, kinds of windows, etc, can make a big difference in cooling your house (I'm assuming in India, heating isn't a big issue). For the solar panels, what's available where you are is a starting point. I will note that in sunny countries, like Turkey and Tunisia, I see a lot of solar hot water on roofs, but not so many solar panels.

Build a two story with a garage under the top story. It will have to be long and narrow lot is not wide. 4 bedrm s will be tight, looks like you only have rm for about 1200 sq ft incl garage. Or you could put front door on side behind garage and stairs inside to go up to bedrooms and bath rooms. Have a small bathroom downstairs. With living area and kitchen, with dining area.