Ignoring the attempts of creationists to derail yet another thread, the current consensus is the entire universe (as opposed to the observable universe) is either very large or infinite in size as it is flat with a measured curvature of near zero.
This needs to be treated with caution however as there are other surfaces which are topologically flat but are finite sized such as a torus.
The curvature can calculated by measuring the hot and cold spots in the CMB (cosmic microwave background) by decomposing the signal from the CMB into various scales as explained in this
post.
These hot and cold spots have an apparent size ~1⁰ in diameter and are produced by sound waves caused by plasma oscillations undergoing compression and rarefaction travelling through the hot ionized gas in the early universe at a known speed v = c/√3 where c is the speed of light for a known length of time (375,000 years).
The angular separation between the hot and cold spots caused by compression and rarefaction respectively corresponds to the wavelength of the sound wave which means the actual size of the hot and cold spots can be calculated.
When the universe cooled down and became transparent these hot and cold spots became permanent records in the CMB.
By comparing the apparent size of the spots to their known actual size, the curvature of the light path between the CMB and the observer and therefore the geometry of the universe can be determined.
It is found from the light paths the apparent and actual diameters are based on triangulation where the angles add up to 180⁰ which is a property of flat space hence the evidence points to scenario (b) indicating a possibly infinitely large universe.
If you want to talk about the shape and size of space you'll need it.
