The guitar is made from one plank of hardwood. I used maple, but you can, in principle use any well-seasoned hardwood plank. Mahogany, walnut, cherry, oak, beech, alder, basswood could all be used just as well as any tropical hardwood I may not even have heard of. Therefore, my standard answer to the question "Can I use this particular type of wood?" is inevitably, "Why not? Give it a try." Even softwood timbers like spruce or pine are conceivable, although hardwood is preferable. Each piece of wood will sound different, but it is practically impossible to predict exactly how. You would have to build several guitars and fit the same electronics, pickup and strings on all of them to be able to compare them. But why should you anyway? I'm quite sure you'll love the sound of your unique lap steel guitar.
Use only dry wood
The wood has to dry before use; otherwise it will warp and not maintain its shape over time. For instrument-making the moisture content ought to not exceed 8% (just in case that you have access to a wood moisture meter). There is a very simple method of making sure that the wood is dry enough: put the pre-dried guitar plank into a room where humidity is below 50% - this can be your workshop or any other room with constant humidity. Weigh the plank and note its weight and the date of weighing on it. Do this once a week until the weight remains constant (i.e., the piece doesn't lose any more weight). This is the point when the wood is in balance with the room and is ready for use.
Wood moisture content
The weight of a piece of wood always includes the weight of the water contained in it. The relative wood moisture content is the ratio between the weight of the water contained in wood and the fully-seasoned wood. The approximate wood moisture content can be determined with electronic measuring instruments measuring the electrical conductivity of wood, which is directly linked to the wood moisture content.