Clay and straw where do I get them

Just about any general merchant for straw, clay you get from your steward.

Edit: There are clay deposits also near your houses which you can mine.

Or you can just get the Clay from Clay deposites, Unlike Mining deposites, you can get an infinite amount of clay from 1 spot.

There's usually at least 1 Clay & Quarried Stone deposite near your Owned Land.

The really difficult material is goat horn. There aren't many horns at a given vendor so buy as many as possible at each visit. You'll need 30 or so for all the wall sconces, chandeliers, etc.

Also buy glass, you'll need it for display cases, lights, etc.

Edit: Also - mine/purchase a dozen to fifteen Corundum ingots, you'll need them to make locks for doors, chests etc.

lakeview manor I am updating my house to buy cows and stuff I have to go to the steward of falkreath? because I went there and she doesn't have any option to buy livestock

You have to have a steward at your HF home, any follower will do in a pinch or you can make your Falkreath Housecarl your steward there. The Jarl's steward has nothing to do with your HF houses, you must promote a follower to be the steward of YOUR house.

Edit: Once you have an established steward at Lakeview you can buy Lumber, clay and finished stone from them. This allows you to continue your construction.

Iron ore (Lots and lots of it) and corundum ore to combine with iron to make locks will have to be mined or bought.

Straw you can buy as noted along with glass at a general merchant. You can also buy goats horns from merchants and/or harvest them from goats you kill.

where do I find a steward

You can take any of your followers to Lakeview and offer them the job. If you are thane of Falkreath hold Rayya is your housecarl and you can offer the job to her. If you are not thane and have no followers you will need to get one by becoming thane somewhere or by doing a friendship/fetch quest for someone. That or become the leader of a faction which will net you multiple followers. Some followers are better stewards than others, I normally in the past have just promoted the housecarl of that particular house and have had no issues with them.

Just be careful - once you have a steward, you'll have the option to let them decorate the house. They'll ask for money and once you give them the go-ahead, they'll fill the rooms with every piece of miscellaney in the game. It'll end up looking like you're a hoarder. It's safer to use the workbench and build stuff yourself.

That has always been my preference, be sure and save before you construct and place an item so that if you don't like the item or where it stands you can revert save and not build it. Display cases are notorious for exploding your display items after hours of painstaking work onto the floor and I find them nearly worthless. I plan on never building any more though there is a process for placing the items that is time consuming. It s your preference though that matters if you want to go through the process.

Also once a Steward is promoted they can not be fired so choose wisely.

understood but you cant buy animals through the workbench

Which is why a steward is a must have which is why he was giving you some wisdom for farther down the line. Concentrate on getting a steward first then you can worry about furnishing your house later.