Ok, so make sure you check out the forum as that is a big key building with includes things like food options, hang-out spots & has the main library. Also, within the forum you'll find the Guild (in the Devonshire House part of the building) which also has lots of seating & the odd food option.
Lovely hang-out spot is Reed Hall Gardens, definitely check that out.
Northcott Theatre (right next to the Guild) is one of the main theatres in the whole city & has a lovely cafe, so that's a nice place to check out.
Also, there are pretty outdoor spaces at the bottom of campus, near the Business School buildings & near the blocks of lafrowda accommodation buildings.
Happy to give more recs on anything else if needed!