Architecture requires one to be from science background (only Maharashtra allows you to be from commerce with math and still opt for architecture by giving entrances)with Physics and Maths as your subjects till 12th. After your 12th you can consider appearing for either NATA (National Aptitude Test for Architecture). There will be two parts to it. The first will be on paper where you need to show your creativity and drawing capabilities. The second will be a computer based test. In this you will be tested on various areas including mental ability, analytical reasoning, creativity, imagination etc. This test will basically test on whether you have the capabilities to be an architect.
You can also appear for AIEEE. The syllabus for AIEE (B.Arch/B.Planning) is as follows:All India Engineering Entrance Examination (AIEEE) B.arch B-planning Syllabus: Part I : Awareness of persons, places, Buildings, Materials.) Objects, Texture related to Architecture and build~ environment. Visualising three dimensional objects from two dimensional drawings. Visualising. different sides of three dimensional objects. Analytical Reasoning Mental Ability (Visual, Numerical and Verbal).
Part II: Three dimensional - perception: Understanding and appreciation of scale and proportion of objects, building forms and elements, colour texture, harmony and contrast. Design and drawing of geometrical or abstract shapes and patterns in pencil. Transformation of forms both 2 D and 3 D union, substraction, rotation, development of surfaces and volumes, Generation of Plan, elevations and 3 D views of objects. Creating two dimensional and three dimensional compositions using given shapes and forms. Sketching of scenes and activities from memory of urbanscape (public space, market, festivals, street
scenes, monuments, recreational spaces etc.), landscape (river fronts, jungles. gardens, trees, plants etc.) and rural life.
You can get a better picture by taking a look at the previous years papers.
Apart from this you can also consider appearing for the state entrance exam for architecture.