This might give you some ideas:
Hi Emmazura. One of the most important things is to find a sturdy piece of furniture since you may need to cut out the center supports if it is a large furniture piece.
Next decide if you want a drop in sink or one that sits on top. If you are considering one that sits on top, measure your furniture piece to ensure that it can either be cut down to the correct height, if necessary.
As for plumbing, flex and pvc piping is easier to work with than rigid metal pipe.
Your next step is to measure (twice!) to make sure any cuts and holes you drill are in the proper positions. Lastly watch a number of videos and choose a simple project for your first time out because mistakes will probably be made. Before long, however, you'll be a pro! Good luck.
To Bijous’ points, a bath vanity top gets exposed to a ton of water, nail polish & remover, essential oils, lipstick and other top-destroying agents.
If you’re going to keep the wood top, put on at least 3 full coats (dried in between) of a Spar Marine varnish or polyurethane.
If you can do this in the garage before you install it, it will be much better, because the off gassing needs to cure with excellent ventilation.
Let it sit another day after the last coat.
Go for it! I bought a second-hand vanity with bench. Added sink on top and above that a mirror from another discarded piece of furniture. It's now my favorite bathroom.