It is usually best to finish a floor before starting construction. Floor finishing is easier and neater when the floor is flat on the table. For some flooring, the extra durability of the finished surface gives needed protection while building .

The first step in finishing a floor is identifying the floor material.  
    Many materials are used in dollhouse floors, and each has its own 'best choices' of finishes and techniques for the look you want   

Veneer flooring has the feel of wood grain on the surface
Not shiny
Brown and not-layered on the edge
(except the flooring layer on the top)
Clear finish    Surface Stain     Paint     Applied Flooring    

MDF is smooth and brown
Not shiny
Brown and granular on the edge - not layered like plywood
Paint        Applied Flooring    Faux-wood floor paint

Scored Plywood has the feel of wood grain on the surface
Not shiny
Shows the 'plys' on the edges
Clear finish    Surface or Penetrating Stain     Paint   

Smooth Plywood has the feel of wood grain on the surface.
Not shiny
Shows the 'plys' on the edges
Clear finish    Surface or Penetrating Stain    Paint   
Stain and Score (make your own flooring) Applied Flooring & Bruce s JM975