Your parents will like whatever you do. It is a very nice thing for a daughter to do.....I would be thrilled.
You can do something simple- get a Duncan Hines cake mix (they are pretty good now days) and then make a homemade icing (or use from a can).

You can decorate with sugared flowers if you want. You will need some edible flowers from the supermarket. Beat up an egg white till foamy (you can do this with a fork) Use a paint brush (clean) or your fingers and paint the flower gently and all over with the egg white. If flower is fragile- gently sprinkle sugar all over - if firmer flower, then dip in the sugar till all coated. Place on a rack to dry and harden a bit and then use on top of the cake. This really looks pretty.....
Good luck- let us know how you make out.