How should i Charge a client for a simple WordPress website? what should i include in the invoice?

There is a lot of factors to think of when pricing your services.

1. How much is your time worth?
2. What sort of client is buying the website? (Obviously a small 2-3 person business is not going to fork out £100 an hour to have a site built unless it is crucial to the running of their business).
3. How long is it going to take you to complete?
4. Does the client require any services such as after purchase support or hosting?
5. What are your costs?
6. How much would you realistically expect the client to want to pay?
7. How much would you pay for it if you were the client?

I do not have set prices with my client work.

1. If I do not like the sound of the project, I am going to quote a higher price, because it doesn't matter if it doesn't get accepted, as the project didn't appeal to me anyway and if it does get accepted I will be getting paid extra for not enjoying what I am doing. (For example, if someone asked me to design a porn website or a gambling website, I wouldn't normally accept this line of work but I will quote them still with a higher price than normal).

2. Some clients are worth giving discounts, for example I recently designed a website for a huge name in the Jewellery Industry who is one of the most connected companies in Hatton Garden that provide services to all the huge brand names. I gave them a shockingly low quote for a huge project I recently completed for them, it was worth more having my name and the connection to the company then any money they could of paid me, it was an instant step in to the top of an industry I had never touched before. It was not a project I was prepared to be out quoted on by another developer.

To answer some of your questions though:

1. I would reccomend supplying a normal invoice with a breakdown of the costs and what the customer is paying for.
2. Write a contract to protect your work, outline any repeat costs for maintanence, hosting and other continued services (you can find hundreds of templates for such contracts on google).
3. I would personally charge per hour for any time consuming services or support required after the site build. I normally give my clients two options, one being a monthly or annual support service they pay for monthly or annually for unlimited support, or I charge hourly for any support needed outside the work outlined in the contract. (I normally offer 3-5 months free support for basic changes and updating to all my clients as well, this is just a selling point I use to build confidence with new clients).

I personally do prefer to quote for a whole project, write up a contract outlining the costs and the work. This way if the client demands extras not included in the contract that could be heavily time consuming I can charge extra so I don't find myself working longer hours for less money. Or if you are going to charge hourly, write up a contract outlining the work, how long each part will take on estimate (over-estimate for safety or you will find yourself working for free).

If you require content, resources or anything from the client to begin work I cant say it enough times in your contract if you give any form of timeline to completion ALWAYS start the time from the clients delivery of what is required. For example: "The project will take 4 months to complete upon receiving the following content 'content here' from 'client here'."

I have had clients not deliver what they promised to deliver 4 months into a project and then moan that the project took longer to complete then estimated. (To be honest I do not think I have ever had a client deliver the content or required resources on time, I cannot stress how important it is to base all your ETA's off of the date you receive everything you require).