This is a question I often get in many different ways from people when I tell them that I am building a plane. To be honest, it is a difficult question to answer. I am not going to say that it is a risk-free venture. But then, crossing street isn't either. The truth of the matter is, it really is up to the builder / pilot. Many of the kits on the market, as well as plans for plans built planes have been around and flying in good numbers. Most of them are good basic designs that have been proven that they can be built and flown safely by novice builders.
Didn't John Denver die in a Homebuilt?
Yes he did. The important fact here is not that the aircraft was a homebuilt. I know there are folks out there who will take issue with me on this one. It was his lack of familiarity with the operation of the aircraft and particular implementation that contributed to his demise. It may sound like semantics, splitting hair to some but there is an important distinction here. There is, however, a very important lesson to be learned from the tragedy. It is extremely important to make sure that the aircraft you are building matches your experiences and flying style. It is nothing new even in the world of certificated aircrafts. Each aircraft design carries with it a unique set of flying characteristics. Some are designed for agility, some are solid IFR platform, and yet others are great bush planes. Each of these characteristics also imposes some skills requirements on the part of pilots who fly them. It is very important that the builder / pilots have skills to match what the aircraft demands. It is the same reason why you should not take off on a Turbo Saratoga in a marginal weather with only few hours on the type and VFR only rating.
Like many other things we do in life, we are faced with many decisions during the construction of Homebuilt aircraft. Even the most complete of the kit leaves a fair amount of decisions to be made by the builder. In fact this is often the very reason many chooses to build rather than simply buy a factory built aircraft. By the very definition of experimental aviation, us builders are granted a large amount of discretion in building of the crafts we fly. In making each decisions, it is important to think through the implication of that particular decision. The first step in the decision process should be this. "Would this compromise the safety of the aircraft in any way?" The safety implication are often multiple. Sometimes they are structural, others aerodynamic, and yet others ergonomic. This is especially true when deviating from kit or plan specifications. Aviation is about carefully managed risks. There is no such thing as 'fool-proof' airplane, homebuilt or otherwise. It is the responsibility of the builder / pilot to assure that the aircraft s/he flies are as safe as can be.
In short, Homebuilt aircraft are safe in the same way as certificated aircrafts are. We need make conscious decisions to keep them that way.