Toilets, Sinks, Showers, Tubs and Disposals - Bathroom has toilet and sink but no shower

I just acquired a live/work space that I eventually plan on moving into full-time. The only problem is the bathroom has no shower, only sink and toilet.
How big of a job is it to install a shower in the bathroom? There is more than ample room to fit a whole size tub but a shower is all I need. What would be the most minimalist way of doing this w it still being done proper? Any info would help thanx

Slab or woof floor? Basement or crawl space below? In a basement? On a second floor?

Its slab floor, no crawl space and single story.

Its slab floor, no crawl space and single story. First you need to determine where the sewer goes under the slab. If you are lucky It runs along the outside and in. In general you are going to need to dig a trench from the sewer line to the edge of the slab where you want the tub. I'd by the tub first so you can be sure where the drain is. You need to cut out a square of slab under the tub at least 15"X15". A circular saw with a diamond dry blade can be used to score the concrete then use a rented pavement breaker (jack hammer) to bust out the concrete.

Once the concrete out you need to dig out to a depth about10" lower then the sewer line. From the trench out side you need to work sideways into the hole you just dug. This hole will hold the P trap for the tub and join with the branch line. You will need to open the wall for installing you water supply and the vent for the tub. OK if you still want to do this the pros can give you more specific information based on what you have plumbing wise.

If the sewer runs under the slab from a distant point and can not be easily reached from outside more slab then just the tub well may need to be cut.