Building is the main skeleton for your empire,even if you are housing your units,producing units,building defence tower or even walls etc,you need to build builing,Wood is always used to build builings
We all would upgrade our building when we have enough resources,but there is ways to save resources while upgrading
1.sell the old item away then buy the upgraded item ---------> for example --------->sell your level 2 tower and you will get back some resources then buy the level three tower
<Attention>!!!!! This method do not work if the next level item require resources to upgrade
2.Wait till the last upgrade of the item then upgrade it--------------> for example -----------------> for your wall,you can wait till you are level 34 then you start building level 5 wall,this saves you lots of stone.
Last word of advise,deciede carefully which resouces it harder to get first,pehaps you would build something that is made of wood or meat which is easier to get rather than stone or gold.Then you may consider building the buildings that require gold or stone to build it later if this is possible
<Attention>!!!!!!! If you are scared that your defences is not nstrong enough,build more level 2 wall,they require 15 wood only each of them compared to 225 stones,stones are very hard to get