There are so many things you can use for walls and floors that are affordable and easy to find.
Let's start with floors.There is a product call WonderFoam. It is used for kids to cut shapes and letters. It can be found in the child craft section of craft stores in 8 1/2 x 11 sheets of many colors. Above is a tile floor I created for my villa. I cut out a bunch of 1 inch by 1 inch squares and glued them down with a small space between to spread the mortar. Then you can faux paint them anyway you want and varnish for some shine. This is great for helping to keep your dollhouse light in weight.
If you want to make a stone patio or path you can spread wood filler with a spackle knife onto a 1/8th thick piece of wood (cut to your shape) then use a tooth pick to mark out the stone pattern. Let dry and sand to perfection. Faux paint it and add some darker paint in the cracks.
You can also pick out a linoleum tile at the hardware store. Score it into the size tile you want with a utility knife. Score long sections first then break those down to smaller pieces. Bend and snap off. Glue down leaving a small space for mortar or glue really close together.
Wood floor sheets can be bought in the miniature section of AC Moore or on internet miniature stores. You can stain them or paint them. If you paint them be sure to fold each scored plank and sand paper them a bit after the paint dries so when you lay it flat there is a definition of space between each plank. The paint will fill in the cracks if you don't.
To make grass you can use terrycloth and paint it for more texture or you can buy dried panels of moss and piece them together. Moss is shown on the right. You can get the Moss at craft stores.
For a gravel path I used sesame seeds. I used unseasoned ones. If your dollhouse will be in a place where mice might be looking for nibbles. I wouldn't recommend this technique, your path may be gone the next morning. : ) Spread white glue down and sprinkle seeds down. Flatten them out with something you can use like a stamp for pressing (not to hard). Go back and fill in areas after the 1st batch dries.
Carpets: Towels are great for shag carpet. Use No Fray on the edges. I have found a ribbon style called Jacquards is great for runners or stair carpet. Finish off the cut ends with matching thin trimmings.
If you have a tropical setting and want rattan or wicker for your rugs, place mats and thin coasters are great! And of course a doily for an area rug in any style house.
Walls....You can obviously buy dollhouse wallpaper but you can also use Scrapbook paper!
I love Martha Stewart's paper! I have just come up with the idea of using ribbon for border wallpaper. We'll see how it works. The smaller the print the better.
So if you want a stucco effect, I would recommend Pre-mixed Tile adhesive and Grout. Spread it on thin with a putty knife, you have to practice with it a bit to get the right texture. Then paint when its dry.
If you want a lot of that texture in your house but don't want the house to get to be too heavy in weight I would suggest sand paper sheets. I used a medium grit, #60-#80. It is a bit of a challenge to work with but worth it. I used wood glue and spread it all around on the back of the sheets but left some places without glue so it would pop out from the wall in places to look a bit more rustic. Where the sheet seams joined I filled it in with some of the grout I mentioned earlier. You have to add grout here and there all over the wall so it's not a straight line where the sand paper sheets join. Try and make the joints minimal above the windows and doors. Then paint. It can be hard on your hands so when you burnish the sandpaper to adhere to the wall, put notebook paper on top of the sandpaper so you don't tear up your hands.
Hopefully some of this will help you create your master piece!