Investment property lacks bathrooms on each level

[Marlin Q. Parker, Sr., Esq.]

Our 4 story investment property only has two baths. The basement is open with a full bath (we recently added during a sewer upgrade); the 1st level contains the kitchen, living, dining, and mud rooms; the 2nd level contains two beds and one full bath; the third level contains two full bedrooms (a large, nicely converted attic).  We are contemplating adding a full bathroom to the top level because it is doubtful that renters would choose to descend a flight a stairs to use the bathroom. We have already run over budget on renovations; furthermore, that particular rental market doesn't produce high yields and such an addition is costly. Should we add the bathroom now (changing to a 4br, 3 bath) or should we wait until we have tenants occupying the property for a few years (allowing the rent to pay for the addition)?