Do you want a motorhome or motorcaravan? If you have the money you can go out and buy one and it should be ready to use from the moment you have it. It could be even faster to rent one. You will be paying for someone else's design and build work, and have to live in their view of the world, but hopefully you will get what you want. If you rent one then you can determine if this is the vehicle for you, and perhaps decide not, or even you don't like the idea. Circumstances may say that you will always rent, but ultimately if this is all that you require then the rest of this site won't be of much value to you. If going down this route, spend time looking at a variety of motorhomes in dealers to get a feel for what layouts and features are available, get the dealers to explain how everything works before you buy, talk to owners, do try one out and I hope you enjoy yourselves in whatever you end up with.
Some reasons to be building:
Building a motorhome requires determination, time and most of all, a vision. It also requires a degree of humility because unless you know everything about the subject, then you will need to ask someone for advice or assistance at sometime. It's a well trodden path now, so there is lots of advice about, (you're reading this) and providing you're not in a hurry, you can take your time to get advice from several sources.
I've said it elsewhere, but join a self build club like the SBMCC and the cost of membership will be recouped in discounts, helpful advice and a bit of comradery.
Inevitably it costs money, unless you are really fortunate with gifts, but the budget can be low and can often be a tradeoff between how much work you can do yourself and how much you can buy. A new base vehicle might cost a lot, but requires no mechanical work, a second-hand van will be cheaper but may require some preparation and repair, and a 20-year old scrapper may keep you busy for weeks before it's drivable. The same applies to furniture and equipment so set a budget and divide up the costs. There can also be a desire to do everything, but be realistic, do you want to build a van for the sake of doing it, or so that you can use it. If you plan to make your van useable at all times then you can go off and enjoy it on trips away and not be worried about it must be complete for the holidays. You can also learn how best to enjoy it and change your design as you go along.